oxedyne/fe2o3/fe2o3_text/tests/annealer_corpus/std_option.rs
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| 1 | //! Optional values. |
| 2 | //! |
| 3 | //! Type [`Option`] represents an optional value: every [`Option`] |
| 4 | //! is either [`Some`] and contains a value, or [`None`], and |
| 5 | //! does not. [`Option`] types are very common in Rust code, as |
| 6 | //! they have a number of uses: |
| 7 | //! |
| 8 | //! * Initial values |
| 9 | //! * Return values for functions that are not defined |
| 10 | //! over their entire input range (partial functions) |
| 11 | //! * Return value for otherwise reporting simple errors, where [`None`] is |
| 12 | //! returned on error |
| 13 | //! * Optional struct fields |
| 14 | //! * Struct fields that can be loaned or "taken" |
| 15 | //! * Optional function arguments |
| 16 | //! * Nullable pointers |
| 17 | //! * Swapping things out of difficult situations |
| 18 | //! |
| 19 | //! [`Option`]s are commonly paired with pattern matching to query the presence |
| 20 | //! of a value and take action, always accounting for the [`None`] case. |
| 21 | //! |
| 22 | //! ``` |
| 23 | //! fn divide(numerator: f64, denominator: f64) -> Option<f64> { |
| 24 | //! if denominator == 0.0 { |
| 25 | //! None |
| 26 | //! } else { |
| 27 | //! Some(numerator / denominator) |
| 28 | //! } |
| 29 | //! } |
| 30 | //! |
| 31 | //! // The return value of the function is an option |
| 32 | //! let result = divide(2.0, 3.0); |
| 33 | //! |
| 34 | //! // Pattern match to retrieve the value |
| 35 | //! match result { |
| 36 | //! // The division was valid |
| 37 | //! Some(x) => println!("Result: {x}"), |
| 38 | //! // The division was invalid |
| 39 | //! None => println!("Cannot divide by 0"), |
| 40 | //! } |
| 41 | //! ``` |
| 42 | //! |
| 43 | //! # Options and pointers ("nullable" pointers) |
| 44 | //! |
| 45 | //! Rust's pointer types must always point to a valid location; there are |
| 46 | //! no "null" references. Instead, Rust has *optional* pointers, like |
| 47 | //! the optional owned box, <code>[Option]<[Box\<T>]></code>. |
| 48 | //! |
| 49 | //! [Box\<T>]: ../../std/boxed/struct.Box.html |
| 50 | //! |
| 51 | //! The following example uses [`Option`] to create an optional box of |
| 52 | //! [`i32`]. Notice that in order to use the inner [`i32`] value, the |
| 53 | //! `check_optional` function first needs to use pattern matching to |
| 54 | //! determine whether the box has a value (i.e., it is [`Some(...)`][`Some`]) or |
| 55 | //! not ([`None`]). |
| 56 | //! |
| 57 | //! ``` |
| 58 | //! let optional = None; |
| 59 | //! check_optional(optional); |
| 60 | //! |
| 61 | //! let optional = Some(Box::new(9000)); |
| 62 | //! check_optional(optional); |
| 63 | //! |
| 64 | //! fn check_optional(optional: Option<Box<i32>>) { |
| 65 | //! match optional { |
| 66 | //! Some(p) => println!("has value {p}"), |
| 67 | //! None => println!("has no value"), |
| 68 | //! } |
| 69 | //! } |
| 70 | //! ``` |
| 71 | //! |
| 72 | //! # The question mark operator, `?` |
| 73 | //! |
| 74 | //! Similar to the [`Result`] type, when writing code that calls many functions that return the |
| 75 | //! [`Option`] type, handling `Some`/`None` can be tedious. The question mark |
| 76 | //! operator, [`?`], hides some of the boilerplate of propagating values |
| 77 | //! up the call stack. |
| 78 | //! |
| 79 | //! It replaces this: |
| 80 | //! |
| 81 | //! ``` |
| 82 | //! # #![allow(dead_code)] |
| 83 | //! fn add_last_numbers(stack: &mut Vec<i32>) -> Option<i32> { |
| 84 | //! let a = stack.pop(); |
| 85 | //! let b = stack.pop(); |
| 86 | //! |
| 87 | //! match (a, b) { |
| 88 | //! (Some(x), Some(y)) => Some(x + y), |
| 89 | //! _ => None, |
| 90 | //! } |
| 91 | //! } |
| 92 | //! |
| 93 | //! ``` |
| 94 | //! |
| 95 | //! With this: |
| 96 | //! |
| 97 | //! ``` |
| 98 | //! # #![allow(dead_code)] |
| 99 | //! fn add_last_numbers(stack: &mut Vec<i32>) -> Option<i32> { |
| 100 | //! Some(stack.pop()? + stack.pop()?) |
| 101 | //! } |
| 102 | //! ``` |
| 103 | //! |
| 104 | //! *It's much nicer!* |
| 105 | //! |
| 106 | //! Ending the expression with [`?`] will result in the [`Some`]'s unwrapped value, unless the |
| 107 | //! result is [`None`], in which case [`None`] is returned early from the enclosing function. |
| 108 | //! |
| 109 | //! [`?`] can be used in functions that return [`Option`] because of the |
| 110 | //! early return of [`None`] that it provides. |
| 111 | //! |
| 112 | //! [`?`]: crate::ops::Try |
| 113 | //! [`Some`]: Some |
| 114 | //! [`None`]: None |
| 115 | //! |
| 116 | //! # Representation |
| 117 | //! |
| 118 | //! Rust guarantees to optimize the following types `T` such that [`Option<T>`] |
| 119 | //! has the same size, alignment, and [function call ABI] as `T`. It is |
| 120 | //! therefore sound, when `T` is one of these types, to transmute a value `t` of |
| 121 | //! type `T` to type `Option<T>` (producing the value `Some(t)`) and to |
| 122 | //! transmute a value `Some(t)` of type `Option<T>` to type `T` (producing the |
| 123 | //! value `t`). |
| 124 | //! |
| 125 | //! In some of these cases, Rust further guarantees the following: |
| 126 | //! - `transmute::<_, Option<T>>([0u8; size_of::<T>()])` is sound and produces |
| 127 | //! `Option::<T>::None` |
| 128 | //! - `transmute::<_, [u8; size_of::<T>()]>(Option::<T>::None)` is sound and produces |
| 129 | //! `[0u8; size_of::<T>()]` |
| 130 | //! |
| 131 | //! These cases are identified by the second column: |
| 132 | //! |
| 133 | //! | `T` | Transmuting between `[0u8; size_of::<T>()]` and `Option::<T>::None` sound? | |
| 134 | //! |---------------------------------------------------------------------|----------------------------------------------------------------------------| |
| 135 | //! | [`Box<U>`] (specifically, only `Box<U, Global>`) | when `U: Sized` | |
| 136 | //! | `&U` | when `U: Sized` | |
| 137 | //! | `&mut U` | when `U: Sized` | |
| 138 | //! | `fn`, `extern "C" fn`[^extern_fn] | always | |
| 139 | //! | [`num::NonZero*`] | always | |
| 140 | //! | [`ptr::NonNull<U>`] | when `U: Sized` | |
| 141 | //! | `#[repr(transparent)]` struct around one of the types in this list. | when it holds for the inner type | |
| 142 | //! |
| 143 | //! [^extern_fn]: this remains true for `unsafe` variants, any argument/return types, and any other ABI: `[unsafe] extern "abi" fn` (_e.g._, `extern "system" fn`) |
| 144 | //! |
| 145 | //! Under some conditions the above types `T` are also null pointer optimized when wrapped in a [`Result`][result_repr]. |
| 146 | //! |
| 147 | //! [`Box<U>`]: ../../std/boxed/struct.Box.html |
| 148 | //! [`num::NonZero*`]: crate::num |
| 149 | //! [`ptr::NonNull<U>`]: crate::ptr::NonNull |
| 150 | //! [function call ABI]: ../primitive.fn.html#abi-compatibility |
| 151 | //! [result_repr]: crate::result#representation |
| 152 | //! |
| 153 | //! This is called the "null pointer optimization" or NPO. |
| 154 | //! |
| 155 | //! It is further guaranteed that, for the cases above, one can |
| 156 | //! [`mem::transmute`] from all valid values of `T` to `Option<T>` and |
| 157 | //! from `Some::<T>(_)` to `T` (but transmuting `None::<T>` to `T` |
| 158 | //! is undefined behavior). |
| 159 | //! |
| 160 | //! # Method overview |
| 161 | //! |
| 162 | //! In addition to working with pattern matching, [`Option`] provides a wide |
| 163 | //! variety of different methods. |
| 164 | //! |
| 165 | //! ## Querying the variant |
| 166 | //! |
| 167 | //! The [`is_some`] and [`is_none`] methods return [`true`] if the [`Option`] |
| 168 | //! is [`Some`] or [`None`], respectively. |
| 169 | //! |
| 170 | //! The [`is_some_and`] and [`is_none_or`] methods apply the provided function |
| 171 | //! to the contents of the [`Option`] to produce a boolean value. |
| 172 | //! If this is [`None`] then a default result is returned instead without executing the function. |
| 173 | //! |
| 174 | //! [`is_none`]: Option::is_none |
| 175 | //! [`is_some`]: Option::is_some |
| 176 | //! [`is_some_and`]: Option::is_some_and |
| 177 | //! [`is_none_or`]: Option::is_none_or |
| 178 | //! |
| 179 | //! ## Adapters for working with references |
| 180 | //! |
| 181 | //! * [`as_ref`] converts from <code>[&][][Option]\<T></code> to <code>[Option]<[&]T></code> |
| 182 | //! * [`as_mut`] converts from <code>[&mut] [Option]\<T></code> to <code>[Option]<[&mut] T></code> |
| 183 | //! * [`as_deref`] converts from <code>[&][][Option]\<T></code> to |
| 184 | //! <code>[Option]<[&]T::[Target]></code> |
| 185 | //! * [`as_deref_mut`] converts from <code>[&mut] [Option]\<T></code> to |
| 186 | //! <code>[Option]<[&mut] T::[Target]></code> |
| 187 | //! * [`as_pin_ref`] converts from <code>[Pin]<[&][][Option]\<T>></code> to |
| 188 | //! <code>[Option]<[Pin]<[&]T>></code> |
| 189 | //! * [`as_pin_mut`] converts from <code>[Pin]<[&mut] [Option]\<T>></code> to |
| 190 | //! <code>[Option]<[Pin]<[&mut] T>></code> |
| 191 | //! * [`as_slice`] returns a one-element slice of the contained value, if any. |
| 192 | //! If this is [`None`], an empty slice is returned. |
| 193 | //! * [`as_mut_slice`] returns a mutable one-element slice of the contained value, if any. |
| 194 | //! If this is [`None`], an empty slice is returned. |
| 195 | //! |
| 196 | //! [&]: reference "shared reference" |
| 197 | //! [&mut]: reference "mutable reference" |
| 198 | //! [Target]: Deref::Target "ops::Deref::Target" |
| 199 | //! [`as_deref`]: Option::as_deref |
| 200 | //! [`as_deref_mut`]: Option::as_deref_mut |
| 201 | //! [`as_mut`]: Option::as_mut |
| 202 | //! [`as_pin_mut`]: Option::as_pin_mut |
| 203 | //! [`as_pin_ref`]: Option::as_pin_ref |
| 204 | //! [`as_ref`]: Option::as_ref |
| 205 | //! [`as_slice`]: Option::as_slice |
| 206 | //! [`as_mut_slice`]: Option::as_mut_slice |
| 207 | //! |
| 208 | //! ## Extracting the contained value |
| 209 | //! |
| 210 | //! These methods extract the contained value in an [`Option<T>`] when it |
| 211 | //! is the [`Some`] variant. If the [`Option`] is [`None`]: |
| 212 | //! |
| 213 | //! * [`expect`] panics with a provided custom message |
| 214 | //! * [`unwrap`] panics with a generic message |
| 215 | //! * [`unwrap_or`] returns the provided default value |
| 216 | //! * [`unwrap_or_default`] returns the default value of the type `T` |
| 217 | //! (which must implement the [`Default`] trait) |
| 218 | //! * [`unwrap_or_else`] returns the result of evaluating the provided |
| 219 | //! function |
| 220 | //! * [`unwrap_unchecked`] produces *[undefined behavior]* |
| 221 | //! |
| 222 | //! [`expect`]: Option::expect |
| 223 | //! [`unwrap`]: Option::unwrap |
| 224 | //! [`unwrap_or`]: Option::unwrap_or |
| 225 | //! [`unwrap_or_default`]: Option::unwrap_or_default |
| 226 | //! [`unwrap_or_else`]: Option::unwrap_or_else |
| 227 | //! [`unwrap_unchecked`]: Option::unwrap_unchecked |
| 228 | //! [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html |
| 229 | //! |
| 230 | //! ## Transforming contained values |
| 231 | //! |
| 232 | //! These methods transform [`Option`] to [`Result`]: |
| 233 | //! |
| 234 | //! * [`ok_or`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to |
| 235 | //! [`Err(err)`] using the provided default `err` value |
| 236 | //! * [`ok_or_else`] transforms [`Some(v)`] to [`Ok(v)`], and [`None`] to |
| 237 | //! a value of [`Err`] using the provided function |
| 238 | //! * [`transpose`] transposes an [`Option`] of a [`Result`] into a |
| 239 | //! [`Result`] of an [`Option`] |
| 240 | //! |
| 241 | //! [`Err(err)`]: Err |
| 242 | //! [`Ok(v)`]: Ok |
| 243 | //! [`Some(v)`]: Some |
| 244 | //! [`ok_or`]: Option::ok_or |
| 245 | //! [`ok_or_else`]: Option::ok_or_else |
| 246 | //! [`transpose`]: Option::transpose |
| 247 | //! |
| 248 | //! These methods transform the [`Some`] variant: |
| 249 | //! |
| 250 | //! * [`filter`] calls the provided predicate function on the contained |
| 251 | //! value `t` if the [`Option`] is [`Some(t)`], and returns [`Some(t)`] |
| 252 | //! if the function returns `true`; otherwise, returns [`None`] |
| 253 | //! * [`flatten`] removes one level of nesting from an [`Option<Option<T>>`] |
| 254 | //! * [`inspect`] method takes ownership of the [`Option`] and applies |
| 255 | //! the provided function to the contained value by reference if [`Some`] |
| 256 | //! * [`map`] transforms [`Option<T>`] to [`Option<U>`] by applying the |
| 257 | //! provided function to the contained value of [`Some`] and leaving |
| 258 | //! [`None`] values unchanged |
| 259 | //! |
| 260 | //! [`Some(t)`]: Some |
| 261 | //! [`filter`]: Option::filter |
| 262 | //! [`flatten`]: Option::flatten |
| 263 | //! [`inspect`]: Option::inspect |
| 264 | //! [`map`]: Option::map |
| 265 | //! |
| 266 | //! These methods transform [`Option<T>`] to a value of a possibly |
| 267 | //! different type `U`: |
| 268 | //! |
| 269 | //! * [`map_or`] applies the provided function to the contained value of |
| 270 | //! [`Some`], or returns the provided default value if the [`Option`] is |
| 271 | //! [`None`] |
| 272 | //! * [`map_or_else`] applies the provided function to the contained value |
| 273 | //! of [`Some`], or returns the result of evaluating the provided |
| 274 | //! fallback function if the [`Option`] is [`None`] |
| 275 | //! |
| 276 | //! [`map_or`]: Option::map_or |
| 277 | //! [`map_or_else`]: Option::map_or_else |
| 278 | //! |
| 279 | //! These methods combine the [`Some`] variants of two [`Option`] values: |
| 280 | //! |
| 281 | //! * [`zip`] returns [`Some((s, o))`] if `self` is [`Some(s)`] and the |
| 282 | //! provided [`Option`] value is [`Some(o)`]; otherwise, returns [`None`] |
| 283 | //! * [`zip_with`] calls the provided function `f` and returns |
| 284 | //! [`Some(f(s, o))`] if `self` is [`Some(s)`] and the provided |
| 285 | //! [`Option`] value is [`Some(o)`]; otherwise, returns [`None`] |
| 286 | //! |
| 287 | //! [`Some(f(s, o))`]: Some |
| 288 | //! [`Some(o)`]: Some |
| 289 | //! [`Some(s)`]: Some |
| 290 | //! [`Some((s, o))`]: Some |
| 291 | //! [`zip`]: Option::zip |
| 292 | //! [`zip_with`]: Option::zip_with |
| 293 | //! |
| 294 | //! ## Boolean operators |
| 295 | //! |
| 296 | //! These methods treat the [`Option`] as a boolean value, where [`Some`] |
| 297 | //! acts like [`true`] and [`None`] acts like [`false`]. There are two |
| 298 | //! categories of these methods: ones that take an [`Option`] as input, and |
| 299 | //! ones that take a function as input (to be lazily evaluated). |
| 300 | //! |
| 301 | //! The [`and`], [`or`], and [`xor`] methods take another [`Option`] as |
| 302 | //! input, and produce an [`Option`] as output. Only the [`and`] method can |
| 303 | //! produce an [`Option<U>`] value having a different inner type `U` than |
| 304 | //! [`Option<T>`]. |
| 305 | //! |
| 306 | //! | method | self | input | output | |
| 307 | //! |---------|-----------|-----------|-----------| |
| 308 | //! | [`and`] | `None` | (ignored) | `None` | |
| 309 | //! | [`and`] | `Some(x)` | `None` | `None` | |
| 310 | //! | [`and`] | `Some(x)` | `Some(y)` | `Some(y)` | |
| 311 | //! | [`or`] | `None` | `None` | `None` | |
| 312 | //! | [`or`] | `None` | `Some(y)` | `Some(y)` | |
| 313 | //! | [`or`] | `Some(x)` | (ignored) | `Some(x)` | |
| 314 | //! | [`xor`] | `None` | `None` | `None` | |
| 315 | //! | [`xor`] | `None` | `Some(y)` | `Some(y)` | |
| 316 | //! | [`xor`] | `Some(x)` | `None` | `Some(x)` | |
| 317 | //! | [`xor`] | `Some(x)` | `Some(y)` | `None` | |
| 318 | //! |
| 319 | //! [`and`]: Option::and |
| 320 | //! [`or`]: Option::or |
| 321 | //! [`xor`]: Option::xor |
| 322 | //! |
| 323 | //! The [`and_then`] and [`or_else`] methods take a function as input, and |
| 324 | //! only evaluate the function when they need to produce a new value. Only |
| 325 | //! the [`and_then`] method can produce an [`Option<U>`] value having a |
| 326 | //! different inner type `U` than [`Option<T>`]. |
| 327 | //! |
| 328 | //! | method | self | function input | function result | output | |
| 329 | //! |--------------|-----------|----------------|-----------------|-----------| |
| 330 | //! | [`and_then`] | `None` | (not provided) | (not evaluated) | `None` | |
| 331 | //! | [`and_then`] | `Some(x)` | `x` | `None` | `None` | |
| 332 | //! | [`and_then`] | `Some(x)` | `x` | `Some(y)` | `Some(y)` | |
| 333 | //! | [`or_else`] | `None` | (not provided) | `None` | `None` | |
| 334 | //! | [`or_else`] | `None` | (not provided) | `Some(y)` | `Some(y)` | |
| 335 | //! | [`or_else`] | `Some(x)` | (not provided) | (not evaluated) | `Some(x)` | |
| 336 | //! |
| 337 | //! [`and_then`]: Option::and_then |
| 338 | //! [`or_else`]: Option::or_else |
| 339 | //! |
| 340 | //! This is an example of using methods like [`and_then`] and [`or`] in a |
| 341 | //! pipeline of method calls. Early stages of the pipeline pass failure |
| 342 | //! values ([`None`]) through unchanged, and continue processing on |
| 343 | //! success values ([`Some`]). Toward the end, [`or`] substitutes an error |
| 344 | //! message if it receives [`None`]. |
| 345 | //! |
| 346 | //! ``` |
| 347 | //! # use std::collections::BTreeMap; |
| 348 | //! let mut bt = BTreeMap::new(); |
| 349 | //! bt.insert(20u8, "foo"); |
| 350 | //! bt.insert(42u8, "bar"); |
| 351 | //! let res = [0u8, 1, 11, 200, 22] |
| 352 | //! .into_iter() |
| 353 | //! .map(|x| { |
| 354 | //! // `checked_sub()` returns `None` on error |
| 355 | //! x.checked_sub(1) |
| 356 | //! // same with `checked_mul()` |
| 357 | //! .and_then(|x| x.checked_mul(2)) |
| 358 | //! // `BTreeMap::get` returns `None` on error |
| 359 | //! .and_then(|x| bt.get(&x)) |
| 360 | //! // Substitute an error message if we have `None` so far |
| 361 | //! .or(Some(&"error!")) |
| 362 | //! .copied() |
| 363 | //! // Won't panic because we unconditionally used `Some` above |
| 364 | //! .unwrap() |
| 365 | //! }) |
| 366 | //! .collect::<Vec<_>>(); |
| 367 | //! assert_eq!(res, ["error!", "error!", "foo", "error!", "bar"]); |
| 368 | //! ``` |
| 369 | //! |
| 370 | //! ## Comparison operators |
| 371 | //! |
| 372 | //! If `T` implements [`PartialOrd`] then [`Option<T>`] will derive its |
| 373 | //! [`PartialOrd`] implementation. With this order, [`None`] compares as |
| 374 | //! less than any [`Some`], and two [`Some`] compare the same way as their |
| 375 | //! contained values would in `T`. If `T` also implements |
| 376 | //! [`Ord`], then so does [`Option<T>`]. |
| 377 | //! |
| 378 | //! ``` |
| 379 | //! assert!(None < Some(0)); |
| 380 | //! assert!(Some(0) < Some(1)); |
| 381 | //! ``` |
| 382 | //! |
| 383 | //! ## Iterating over `Option` |
| 384 | //! |
| 385 | //! An [`Option`] can be iterated over. This can be helpful if you need an |
| 386 | //! iterator that is conditionally empty. The iterator will either produce |
| 387 | //! a single value (when the [`Option`] is [`Some`]), or produce no values |
| 388 | //! (when the [`Option`] is [`None`]). For example, [`into_iter`] acts like |
| 389 | //! [`once(v)`] if the [`Option`] is [`Some(v)`], and like [`empty()`] if |
| 390 | //! the [`Option`] is [`None`]. |
| 391 | //! |
| 392 | //! [`Some(v)`]: Some |
| 393 | //! [`empty()`]: crate::iter::empty |
| 394 | //! [`once(v)`]: crate::iter::once |
| 395 | //! |
| 396 | //! Iterators over [`Option<T>`] come in three types: |
| 397 | //! |
| 398 | //! * [`into_iter`] consumes the [`Option`] and produces the contained |
| 399 | //! value |
| 400 | //! * [`iter`] produces an immutable reference of type `&T` to the |
| 401 | //! contained value |
| 402 | //! * [`iter_mut`] produces a mutable reference of type `&mut T` to the |
| 403 | //! contained value |
| 404 | //! |
| 405 | //! [`into_iter`]: Option::into_iter |
| 406 | //! [`iter`]: Option::iter |
| 407 | //! [`iter_mut`]: Option::iter_mut |
| 408 | //! |
| 409 | //! An iterator over [`Option`] can be useful when chaining iterators, for |
| 410 | //! example, to conditionally insert items. (It's not always necessary to |
| 411 | //! explicitly call an iterator constructor: many [`Iterator`] methods that |
| 412 | //! accept other iterators will also accept iterable types that implement |
| 413 | //! [`IntoIterator`], which includes [`Option`].) |
| 414 | //! |
| 415 | //! ``` |
| 416 | //! let yep = Some(42); |
| 417 | //! let nope = None; |
| 418 | //! // chain() already calls into_iter(), so we don't have to do so |
| 419 | //! let nums: Vec<i32> = (0..4).chain(yep).chain(4..8).collect(); |
| 420 | //! assert_eq!(nums, [0, 1, 2, 3, 42, 4, 5, 6, 7]); |
| 421 | //! let nums: Vec<i32> = (0..4).chain(nope).chain(4..8).collect(); |
| 422 | //! assert_eq!(nums, [0, 1, 2, 3, 4, 5, 6, 7]); |
| 423 | //! ``` |
| 424 | //! |
| 425 | //! One reason to chain iterators in this way is that a function returning |
| 426 | //! `impl Iterator` must have all possible return values be of the same |
| 427 | //! concrete type. Chaining an iterated [`Option`] can help with that. |
| 428 | //! |
| 429 | //! ``` |
| 430 | //! fn make_iter(do_insert: bool) -> impl Iterator<Item = i32> { |
| 431 | //! // Explicit returns to illustrate return types matching |
| 432 | //! match do_insert { |
| 433 | //! true => return (0..4).chain(Some(42)).chain(4..8), |
| 434 | //! false => return (0..4).chain(None).chain(4..8), |
| 435 | //! } |
| 436 | //! } |
| 437 | //! println!("{:?}", make_iter(true).collect::<Vec<_>>()); |
| 438 | //! println!("{:?}", make_iter(false).collect::<Vec<_>>()); |
| 439 | //! ``` |
| 440 | //! |
| 441 | //! If we try to do the same thing, but using [`once()`] and [`empty()`], |
| 442 | //! we can't return `impl Iterator` anymore because the concrete types of |
| 443 | //! the return values differ. |
| 444 | //! |
| 445 | //! [`empty()`]: crate::iter::empty |
| 446 | //! [`once()`]: crate::iter::once |
| 447 | //! |
| 448 | //! ```compile_fail,E0308 |
| 449 | //! # use std::iter::{empty, once}; |
| 450 | //! // This won't compile because all possible returns from the function |
| 451 | //! // must have the same concrete type. |
| 452 | //! fn make_iter(do_insert: bool) -> impl Iterator<Item = i32> { |
| 453 | //! // Explicit returns to illustrate return types not matching |
| 454 | //! match do_insert { |
| 455 | //! true => return (0..4).chain(once(42)).chain(4..8), |
| 456 | //! false => return (0..4).chain(empty()).chain(4..8), |
| 457 | //! } |
| 458 | //! } |
| 459 | //! ``` |
| 460 | //! |
| 461 | //! ## Collecting into `Option` |
| 462 | //! |
| 463 | //! [`Option`] implements the [`FromIterator`][impl-FromIterator] trait, |
| 464 | //! which allows an iterator over [`Option`] values to be collected into an |
| 465 | //! [`Option`] of a collection of each contained value of the original |
| 466 | //! [`Option`] values, or [`None`] if any of the elements was [`None`]. |
| 467 | //! |
| 468 | //! [impl-FromIterator]: Option#impl-FromIterator%3COption%3CA%3E%3E-for-Option%3CV%3E |
| 469 | //! |
| 470 | //! ``` |
| 471 | //! let v = [Some(2), Some(4), None, Some(8)]; |
| 472 | //! let res: Option<Vec<_>> = v.into_iter().collect(); |
| 473 | //! assert_eq!(res, None); |
| 474 | //! let v = [Some(2), Some(4), Some(8)]; |
| 475 | //! let res: Option<Vec<_>> = v.into_iter().collect(); |
| 476 | //! assert_eq!(res, Some(vec![2, 4, 8])); |
| 477 | //! ``` |
| 478 | //! |
| 479 | //! [`Option`] also implements the [`Product`][impl-Product] and |
| 480 | //! [`Sum`][impl-Sum] traits, allowing an iterator over [`Option`] values |
| 481 | //! to provide the [`product`][Iterator::product] and |
| 482 | //! [`sum`][Iterator::sum] methods. |
| 483 | //! |
| 484 | //! [impl-Product]: Option#impl-Product%3COption%3CU%3E%3E-for-Option%3CT%3E |
| 485 | //! [impl-Sum]: Option#impl-Sum%3COption%3CU%3E%3E-for-Option%3CT%3E |
| 486 | //! |
| 487 | //! ``` |
| 488 | //! let v = [None, Some(1), Some(2), Some(3)]; |
| 489 | //! let res: Option<i32> = v.into_iter().sum(); |
| 490 | //! assert_eq!(res, None); |
| 491 | //! let v = [Some(1), Some(2), Some(21)]; |
| 492 | //! let res: Option<i32> = v.into_iter().product(); |
| 493 | //! assert_eq!(res, Some(42)); |
| 494 | //! ``` |
| 495 | //! |
| 496 | //! ## Modifying an [`Option`] in-place |
| 497 | //! |
| 498 | //! These methods return a mutable reference to the contained value of an |
| 499 | //! [`Option<T>`]: |
| 500 | //! |
| 501 | //! * [`insert`] inserts a value, dropping any old contents |
| 502 | //! * [`get_or_insert`] gets the current value, inserting a provided |
| 503 | //! default value if it is [`None`] |
| 504 | //! * [`get_or_insert_default`] gets the current value, inserting the |
| 505 | //! default value of type `T` (which must implement [`Default`]) if it is |
| 506 | //! [`None`] |
| 507 | //! * [`get_or_insert_with`] gets the current value, inserting a default |
| 508 | //! computed by the provided function if it is [`None`] |
| 509 | //! |
| 510 | //! [`get_or_insert`]: Option::get_or_insert |
| 511 | //! [`get_or_insert_default`]: Option::get_or_insert_default |
| 512 | //! [`get_or_insert_with`]: Option::get_or_insert_with |
| 513 | //! [`insert`]: Option::insert |
| 514 | //! |
| 515 | //! These methods transfer ownership of the contained value of an |
| 516 | //! [`Option`]: |
| 517 | //! |
| 518 | //! * [`take`] takes ownership of the contained value of an [`Option`], if |
| 519 | //! any, replacing the [`Option`] with [`None`] |
| 520 | //! * [`replace`] takes ownership of the contained value of an [`Option`], |
| 521 | //! if any, replacing the [`Option`] with a [`Some`] containing the |
| 522 | //! provided value |
| 523 | //! |
| 524 | //! [`replace`]: Option::replace |
| 525 | //! [`take`]: Option::take |
| 526 | //! |
| 527 | //! # Examples |
| 528 | //! |
| 529 | //! Basic pattern matching on [`Option`]: |
| 530 | //! |
| 531 | //! ``` |
| 532 | //! let msg = Some("howdy"); |
| 533 | //! |
| 534 | //! // Take a reference to the contained string |
| 535 | //! if let Some(m) = &msg { |
| 536 | //! println!("{}", *m); |
| 537 | //! } |
| 538 | //! |
| 539 | //! // Remove the contained string, destroying the Option |
| 540 | //! let unwrapped_msg = msg.unwrap_or("default message"); |
| 541 | //! ``` |
| 542 | //! |
| 543 | //! Initialize a result to [`None`] before a loop: |
| 544 | //! |
| 545 | //! ``` |
| 546 | //! enum Kingdom { Plant(u32, &'static str), Animal(u32, &'static str) } |
| 547 | //! |
| 548 | //! // A list of data to search through. |
| 549 | //! let all_the_big_things = [ |
| 550 | //! Kingdom::Plant(250, "redwood"), |
| 551 | //! Kingdom::Plant(230, "noble fir"), |
| 552 | //! Kingdom::Plant(229, "sugar pine"), |
| 553 | //! Kingdom::Animal(25, "blue whale"), |
| 554 | //! Kingdom::Animal(19, "fin whale"), |
| 555 | //! Kingdom::Animal(15, "north pacific right whale"), |
| 556 | //! ]; |
| 557 | //! |
| 558 | //! // We're going to search for the name of the biggest animal, |
| 559 | //! // but to start with we've just got `None`. |
| 560 | //! let mut name_of_biggest_animal = None; |
| 561 | //! let mut size_of_biggest_animal = 0; |
| 562 | //! for big_thing in &all_the_big_things { |
| 563 | //! match *big_thing { |
| 564 | //! Kingdom::Animal(size, name) if size > size_of_biggest_animal => { |
| 565 | //! // Now we've found the name of some big animal |
| 566 | //! size_of_biggest_animal = size; |
| 567 | //! name_of_biggest_animal = Some(name); |
| 568 | //! } |
| 569 | //! Kingdom::Animal(..) | Kingdom::Plant(..) => () |
| 570 | //! } |
| 571 | //! } |
| 572 | //! |
| 573 | //! match name_of_biggest_animal { |
| 574 | //! Some(name) => println!("the biggest animal is {name}"), |
| 575 | //! None => println!("there are no animals :("), |
| 576 | //! } |
| 577 | //! ``` |
| 578 | |
| 579 | #![stable(feature = "rust1", since = "1.0.0")] |
| 580 | |
| 581 | use crate::clone::TrivialClone; |
| 582 | use crate::iter::{self, FusedIterator, TrustedLen}; |
| 583 | use crate::marker::Destruct; |
| 584 | use crate::ops::{self, ControlFlow, Deref, DerefMut, Residual, Try}; |
| 585 | use crate::panicking::{panic, panic_display}; |
| 586 | use crate::pin::Pin; |
| 587 | use crate::{cmp, convert, hint, mem, slice}; |
| 588 | |
| 589 | /// The `Option` type. See [the module level documentation](self) for more. |
| 590 | #[doc(search_unbox)] |
| 591 | #[derive(Copy, Debug, Hash)] |
| 592 | #[derive_const(Eq)] |
| 593 | #[rustc_diagnostic_item = "Option"] |
| 594 | #[lang = "Option"] |
| 595 | #[stable(feature = "rust1", since = "1.0.0")] |
| 596 | #[allow(clippy::derived_hash_with_manual_eq)] // PartialEq is manually implemented equivalently |
| 597 | pub enum Option<T> { |
| 598 | /// No value. |
| 599 | #[lang = "None"] |
| 600 | #[stable(feature = "rust1", since = "1.0.0")] |
| 601 | None, |
| 602 | /// Some value of type `T`. |
| 603 | #[lang = "Some"] |
| 604 | #[stable(feature = "rust1", since = "1.0.0")] |
| 605 | Some(#[stable(feature = "rust1", since = "1.0.0")] T), |
| 606 | } |
| 607 | |
| 608 | ///////////////////////////////////////////////////////////////////////////// |
| 609 | // Type implementation |
| 610 | ///////////////////////////////////////////////////////////////////////////// |
| 611 | |
| 612 | impl<T> Option<T> { |
| 613 | ///////////////////////////////////////////////////////////////////////// |
| 614 | // Querying the contained values |
| 615 | ///////////////////////////////////////////////////////////////////////// |
| 616 | |
| 617 | /// Returns `true` if the option is a [`Some`] value. |
| 618 | /// |
| 619 | /// # Examples |
| 620 | /// |
| 621 | /// ``` |
| 622 | /// let x: Option<u32> = Some(2); |
| 623 | /// assert_eq!(x.is_some(), true); |
| 624 | /// |
| 625 | /// let x: Option<u32> = None; |
| 626 | /// assert_eq!(x.is_some(), false); |
| 627 | /// ``` |
| 628 | #[must_use = "if you intended to assert that this has a value, consider `.unwrap()` instead"] |
| 629 | #[inline] |
| 630 | #[stable(feature = "rust1", since = "1.0.0")] |
| 631 | #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")] |
| 632 | pub const fn is_some(&self) -> bool { |
| 633 | matches!(*self, Some(_)) |
| 634 | } |
| 635 | |
| 636 | /// Returns `true` if the option is a [`Some`] and the value inside of it matches a predicate. |
| 637 | /// |
| 638 | /// # Examples |
| 639 | /// |
| 640 | /// ``` |
| 641 | /// let x: Option<u32> = Some(2); |
| 642 | /// assert_eq!(x.is_some_and(|x| x > 1), true); |
| 643 | /// |
| 644 | /// let x: Option<u32> = Some(0); |
| 645 | /// assert_eq!(x.is_some_and(|x| x > 1), false); |
| 646 | /// |
| 647 | /// let x: Option<u32> = None; |
| 648 | /// assert_eq!(x.is_some_and(|x| x > 1), false); |
| 649 | /// |
| 650 | /// let x: Option<String> = Some("ownership".to_string()); |
| 651 | /// assert_eq!(x.as_ref().is_some_and(|x| x.len() > 1), true); |
| 652 | /// println!("still alive {:?}", x); |
| 653 | /// ``` |
| 654 | #[must_use] |
| 655 | #[inline] |
| 656 | #[stable(feature = "is_some_and", since = "1.70.0")] |
| 657 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 658 | pub const fn is_some_and(self, f: impl [const] FnOnce(T) -> bool + [const] Destruct) -> bool { |
| 659 | match self { |
| 660 | None => false, |
| 661 | Some(x) => f(x), |
| 662 | } |
| 663 | } |
| 664 | |
| 665 | /// Returns `true` if the option is a [`None`] value. |
| 666 | /// |
| 667 | /// # Examples |
| 668 | /// |
| 669 | /// ``` |
| 670 | /// let x: Option<u32> = Some(2); |
| 671 | /// assert_eq!(x.is_none(), false); |
| 672 | /// |
| 673 | /// let x: Option<u32> = None; |
| 674 | /// assert_eq!(x.is_none(), true); |
| 675 | /// ``` |
| 676 | #[must_use = "if you intended to assert that this doesn't have a value, consider \ |
| 677 | wrapping this in an `assert!()` instead"] |
| 678 | #[inline] |
| 679 | #[stable(feature = "rust1", since = "1.0.0")] |
| 680 | #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")] |
| 681 | pub const fn is_none(&self) -> bool { |
| 682 | !self.is_some() |
| 683 | } |
| 684 | |
| 685 | /// Returns `true` if the option is a [`None`] or the value inside of it matches a predicate. |
| 686 | /// |
| 687 | /// # Examples |
| 688 | /// |
| 689 | /// ``` |
| 690 | /// let x: Option<u32> = Some(2); |
| 691 | /// assert_eq!(x.is_none_or(|x| x > 1), true); |
| 692 | /// |
| 693 | /// let x: Option<u32> = Some(0); |
| 694 | /// assert_eq!(x.is_none_or(|x| x > 1), false); |
| 695 | /// |
| 696 | /// let x: Option<u32> = None; |
| 697 | /// assert_eq!(x.is_none_or(|x| x > 1), true); |
| 698 | /// |
| 699 | /// let x: Option<String> = Some("ownership".to_string()); |
| 700 | /// assert_eq!(x.as_ref().is_none_or(|x| x.len() > 1), true); |
| 701 | /// println!("still alive {:?}", x); |
| 702 | /// ``` |
| 703 | #[must_use] |
| 704 | #[inline] |
| 705 | #[stable(feature = "is_none_or", since = "1.82.0")] |
| 706 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 707 | pub const fn is_none_or(self, f: impl [const] FnOnce(T) -> bool + [const] Destruct) -> bool { |
| 708 | match self { |
| 709 | None => true, |
| 710 | Some(x) => f(x), |
| 711 | } |
| 712 | } |
| 713 | |
| 714 | ///////////////////////////////////////////////////////////////////////// |
| 715 | // Adapter for working with references |
| 716 | ///////////////////////////////////////////////////////////////////////// |
| 717 | |
| 718 | /// Converts from `&Option<T>` to `Option<&T>`. |
| 719 | /// |
| 720 | /// # Examples |
| 721 | /// |
| 722 | /// Calculates the length of an <code>Option<[String]></code> as an <code>Option<[usize]></code> |
| 723 | /// without moving the [`String`]. The [`map`] method takes the `self` argument by value, |
| 724 | /// consuming the original, so this technique uses `as_ref` to first take an `Option` to a |
| 725 | /// reference to the value inside the original. |
| 726 | /// |
| 727 | /// [`map`]: Option::map |
| 728 | /// [String]: ../../std/string/struct.String.html "String" |
| 729 | /// [`String`]: ../../std/string/struct.String.html "String" |
| 730 | /// |
| 731 | /// ``` |
| 732 | /// let text: Option<String> = Some("Hello, world!".to_string()); |
| 733 | /// // First, cast `Option<String>` to `Option<&String>` with `as_ref`, |
| 734 | /// // then consume *that* with `map`, leaving `text` on the stack. |
| 735 | /// let text_length: Option<usize> = text.as_ref().map(|s| s.len()); |
| 736 | /// println!("still can print text: {text:?}"); |
| 737 | /// ``` |
| 738 | #[inline] |
| 739 | #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")] |
| 740 | #[stable(feature = "rust1", since = "1.0.0")] |
| 741 | pub const fn as_ref(&self) -> Option<&T> { |
| 742 | match *self { |
| 743 | Some(ref x) => Some(x), |
| 744 | None => None, |
| 745 | } |
| 746 | } |
| 747 | |
| 748 | /// Converts from `&mut Option<T>` to `Option<&mut T>`. |
| 749 | /// |
| 750 | /// # Examples |
| 751 | /// |
| 752 | /// ``` |
| 753 | /// let mut x = Some(2); |
| 754 | /// match x.as_mut() { |
| 755 | /// Some(v) => *v = 42, |
| 756 | /// None => {}, |
| 757 | /// } |
| 758 | /// assert_eq!(x, Some(42)); |
| 759 | /// ``` |
| 760 | #[inline] |
| 761 | #[stable(feature = "rust1", since = "1.0.0")] |
| 762 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 763 | pub const fn as_mut(&mut self) -> Option<&mut T> { |
| 764 | match *self { |
| 765 | Some(ref mut x) => Some(x), |
| 766 | None => None, |
| 767 | } |
| 768 | } |
| 769 | |
| 770 | /// Converts from <code>[Pin]<[&]Option\<T>></code> to <code>Option<[Pin]<[&]T>></code>. |
| 771 | /// |
| 772 | /// [&]: reference "shared reference" |
| 773 | #[inline] |
| 774 | #[must_use] |
| 775 | #[stable(feature = "pin", since = "1.33.0")] |
| 776 | #[rustc_const_stable(feature = "const_option_ext", since = "1.84.0")] |
| 777 | pub const fn as_pin_ref(self: Pin<&Self>) -> Option<Pin<&T>> { |
| 778 | // FIXME(const-hack): use `map` once that is possible |
| 779 | match Pin::get_ref(self).as_ref() { |
| 780 | // SAFETY: `x` is guaranteed to be pinned because it comes from `self` |
| 781 | // which is pinned. |
| 782 | Some(x) => unsafe { Some(Pin::new_unchecked(x)) }, |
| 783 | None => None, |
| 784 | } |
| 785 | } |
| 786 | |
| 787 | /// Converts from <code>[Pin]<[&mut] Option\<T>></code> to <code>Option<[Pin]<[&mut] T>></code>. |
| 788 | /// |
| 789 | /// [&mut]: reference "mutable reference" |
| 790 | #[inline] |
| 791 | #[must_use] |
| 792 | #[stable(feature = "pin", since = "1.33.0")] |
| 793 | #[rustc_const_stable(feature = "const_option_ext", since = "1.84.0")] |
| 794 | pub const fn as_pin_mut(self: Pin<&mut Self>) -> Option<Pin<&mut T>> { |
| 795 | // SAFETY: `get_unchecked_mut` is never used to move the `Option` inside `self`. |
| 796 | // `x` is guaranteed to be pinned because it comes from `self` which is pinned. |
| 797 | unsafe { |
| 798 | // FIXME(const-hack): use `map` once that is possible |
| 799 | match Pin::get_unchecked_mut(self).as_mut() { |
| 800 | Some(x) => Some(Pin::new_unchecked(x)), |
| 801 | None => None, |
| 802 | } |
| 803 | } |
| 804 | } |
| 805 | |
| 806 | #[inline] |
| 807 | const fn len(&self) -> usize { |
| 808 | // Using the intrinsic avoids emitting a branch to get the 0 or 1. |
| 809 | let discriminant: isize = crate::intrinsics::discriminant_value(self); |
| 810 | discriminant as usize |
| 811 | } |
| 812 | |
| 813 | /// Returns a slice of the contained value, if any. If this is `None`, an |
| 814 | /// empty slice is returned. This can be useful to have a single type of |
| 815 | /// iterator over an `Option` or slice. |
| 816 | /// |
| 817 | /// Note: Should you have an `Option<&T>` and wish to get a slice of `T`, |
| 818 | /// you can unpack it via `opt.map_or(&[], std::slice::from_ref)`. |
| 819 | /// |
| 820 | /// # Examples |
| 821 | /// |
| 822 | /// ```rust |
| 823 | /// assert_eq!( |
| 824 | /// [Some(1234).as_slice(), None.as_slice()], |
| 825 | /// [&[1234][..], &[][..]], |
| 826 | /// ); |
| 827 | /// ``` |
| 828 | /// |
| 829 | /// The inverse of this function is (discounting |
| 830 | /// borrowing) [`[_]::first`](slice::first): |
| 831 | /// |
| 832 | /// ```rust |
| 833 | /// for i in [Some(1234_u16), None] { |
| 834 | /// assert_eq!(i.as_ref(), i.as_slice().first()); |
| 835 | /// } |
| 836 | /// ``` |
| 837 | #[inline] |
| 838 | #[must_use] |
| 839 | #[stable(feature = "option_as_slice", since = "1.75.0")] |
| 840 | #[rustc_const_stable(feature = "const_option_ext", since = "1.84.0")] |
| 841 | pub const fn as_slice(&self) -> &[T] { |
| 842 | // SAFETY: When the `Option` is `Some`, we're using the actual pointer |
| 843 | // to the payload, with a length of 1, so this is equivalent to |
| 844 | // `slice::from_ref`, and thus is safe. |
| 845 | // When the `Option` is `None`, the length used is 0, so to be safe it |
| 846 | // just needs to be aligned, which it is because `&self` is aligned and |
| 847 | // the offset used is a multiple of alignment. |
| 848 | // |
| 849 | // Here we assume that `offset_of!` always returns an offset to an |
| 850 | // in-bounds and correctly aligned position for a `T` (even if in the |
| 851 | // `None` case it's just padding). |
| 852 | unsafe { |
| 853 | slice::from_raw_parts( |
| 854 | (self as *const Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(), |
| 855 | self.len(), |
| 856 | ) |
| 857 | } |
| 858 | } |
| 859 | |
| 860 | /// Returns a mutable slice of the contained value, if any. If this is |
| 861 | /// `None`, an empty slice is returned. This can be useful to have a |
| 862 | /// single type of iterator over an `Option` or slice. |
| 863 | /// |
| 864 | /// Note: Should you have an `Option<&mut T>` instead of a |
| 865 | /// `&mut Option<T>`, which this method takes, you can obtain a mutable |
| 866 | /// slice via `opt.map_or(&mut [], std::slice::from_mut)`. |
| 867 | /// |
| 868 | /// # Examples |
| 869 | /// |
| 870 | /// ```rust |
| 871 | /// assert_eq!( |
| 872 | /// [Some(1234).as_mut_slice(), None.as_mut_slice()], |
| 873 | /// [&mut [1234][..], &mut [][..]], |
| 874 | /// ); |
| 875 | /// ``` |
| 876 | /// |
| 877 | /// The result is a mutable slice of zero or one items that points into |
| 878 | /// our original `Option`: |
| 879 | /// |
| 880 | /// ```rust |
| 881 | /// let mut x = Some(1234); |
| 882 | /// x.as_mut_slice()[0] += 1; |
| 883 | /// assert_eq!(x, Some(1235)); |
| 884 | /// ``` |
| 885 | /// |
| 886 | /// The inverse of this method (discounting borrowing) |
| 887 | /// is [`[_]::first_mut`](slice::first_mut): |
| 888 | /// |
| 889 | /// ```rust |
| 890 | /// assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123)) |
| 891 | /// ``` |
| 892 | #[inline] |
| 893 | #[must_use] |
| 894 | #[stable(feature = "option_as_slice", since = "1.75.0")] |
| 895 | #[rustc_const_stable(feature = "const_option_ext", since = "1.84.0")] |
| 896 | pub const fn as_mut_slice(&mut self) -> &mut [T] { |
| 897 | // SAFETY: When the `Option` is `Some`, we're using the actual pointer |
| 898 | // to the payload, with a length of 1, so this is equivalent to |
| 899 | // `slice::from_mut`, and thus is safe. |
| 900 | // When the `Option` is `None`, the length used is 0, so to be safe it |
| 901 | // just needs to be aligned, which it is because `&self` is aligned and |
| 902 | // the offset used is a multiple of alignment. |
| 903 | // |
| 904 | // In the new version, the intrinsic creates a `*const T` from a |
| 905 | // mutable reference so it is safe to cast back to a mutable pointer |
| 906 | // here. As with `as_slice`, the intrinsic always returns a pointer to |
| 907 | // an in-bounds and correctly aligned position for a `T` (even if in |
| 908 | // the `None` case it's just padding). |
| 909 | unsafe { |
| 910 | slice::from_raw_parts_mut( |
| 911 | (self as *mut Self).byte_add(core::mem::offset_of!(Self, Some.0)).cast(), |
| 912 | self.len(), |
| 913 | ) |
| 914 | } |
| 915 | } |
| 916 | |
| 917 | ///////////////////////////////////////////////////////////////////////// |
| 918 | // Getting to contained values |
| 919 | ///////////////////////////////////////////////////////////////////////// |
| 920 | |
| 921 | /// Returns the contained [`Some`] value, consuming the `self` value. |
| 922 | /// |
| 923 | /// # Panics |
| 924 | /// |
| 925 | /// Panics if the value is a [`None`] with a custom panic message provided by |
| 926 | /// `msg`. |
| 927 | /// |
| 928 | /// # Examples |
| 929 | /// |
| 930 | /// ``` |
| 931 | /// let x = Some("value"); |
| 932 | /// assert_eq!(x.expect("fruits are healthy"), "value"); |
| 933 | /// ``` |
| 934 | /// |
| 935 | /// ```should_panic |
| 936 | /// let x: Option<&str> = None; |
| 937 | /// x.expect("fruits are healthy"); // panics with `fruits are healthy` |
| 938 | /// ``` |
| 939 | /// |
| 940 | /// # Recommended Message Style |
| 941 | /// |
| 942 | /// We recommend that `expect` messages are used to describe the reason you |
| 943 | /// _expect_ the `Option` should be `Some`. |
| 944 | /// |
| 945 | /// ```should_panic |
| 946 | /// # let slice: &[u8] = &[]; |
| 947 | /// let item = slice.get(0) |
| 948 | /// .expect("slice should not be empty"); |
| 949 | /// ``` |
| 950 | /// |
| 951 | /// **Hint**: If you're having trouble remembering how to phrase expect |
| 952 | /// error messages remember to focus on the word "should" as in "env |
| 953 | /// variable should be set by blah" or "the given binary should be available |
| 954 | /// and executable by the current user". |
| 955 | /// |
| 956 | /// For more detail on expect message styles and the reasoning behind our |
| 957 | /// recommendation please refer to the section on ["Common Message |
| 958 | /// Styles"](../../std/error/index.html#common-message-styles) in the [`std::error`](../../std/error/index.html) module docs. |
| 959 | #[inline] |
| 960 | #[track_caller] |
| 961 | #[stable(feature = "rust1", since = "1.0.0")] |
| 962 | #[rustc_diagnostic_item = "option_expect"] |
| 963 | #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 964 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 965 | pub const fn expect(self, msg: &str) -> T { |
| 966 | match self { |
| 967 | Some(val) => val, |
| 968 | None => expect_failed(msg), |
| 969 | } |
| 970 | } |
| 971 | |
| 972 | /// Returns the contained [`Some`] value, consuming the `self` value. |
| 973 | /// |
| 974 | /// Because this function may panic, its use is generally discouraged. |
| 975 | /// Panics are meant for unrecoverable errors, and |
| 976 | /// [may abort the entire program][panic-abort]. |
| 977 | /// |
| 978 | /// Instead, prefer to use pattern matching and handle the [`None`] |
| 979 | /// case explicitly, or call [`unwrap_or`], [`unwrap_or_else`], or |
| 980 | /// [`unwrap_or_default`]. In functions returning `Option`, you can use |
| 981 | /// [the `?` (try) operator][try-option]. |
| 982 | /// |
| 983 | /// [panic-abort]: https://doc.rust-lang.org/book/ch09-01-unrecoverable-errors-with-panic.html |
| 984 | /// [try-option]: https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html#where-the--operator-can-be-used |
| 985 | /// [`unwrap_or`]: Option::unwrap_or |
| 986 | /// [`unwrap_or_else`]: Option::unwrap_or_else |
| 987 | /// [`unwrap_or_default`]: Option::unwrap_or_default |
| 988 | /// |
| 989 | /// # Panics |
| 990 | /// |
| 991 | /// Panics if the self value equals [`None`]. |
| 992 | /// |
| 993 | /// # Examples |
| 994 | /// |
| 995 | /// ``` |
| 996 | /// let x = Some("air"); |
| 997 | /// assert_eq!(x.unwrap(), "air"); |
| 998 | /// ``` |
| 999 | /// |
| 1000 | /// ```should_panic |
| 1001 | /// let x: Option<&str> = None; |
| 1002 | /// assert_eq!(x.unwrap(), "air"); // fails |
| 1003 | /// ``` |
| 1004 | #[inline(always)] |
| 1005 | #[track_caller] |
| 1006 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1007 | #[rustc_diagnostic_item = "option_unwrap"] |
| 1008 | #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 1009 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 1010 | pub const fn unwrap(self) -> T { |
| 1011 | match self { |
| 1012 | Some(val) => val, |
| 1013 | None => unwrap_failed(), |
| 1014 | } |
| 1015 | } |
| 1016 | |
| 1017 | /// Returns the contained [`Some`] value or a provided default. |
| 1018 | /// |
| 1019 | /// Arguments passed to `unwrap_or` are eagerly evaluated; if you are passing |
| 1020 | /// the result of a function call, it is recommended to use [`unwrap_or_else`], |
| 1021 | /// which is lazily evaluated. |
| 1022 | /// |
| 1023 | /// [`unwrap_or_else`]: Option::unwrap_or_else |
| 1024 | /// |
| 1025 | /// # Examples |
| 1026 | /// |
| 1027 | /// ``` |
| 1028 | /// assert_eq!(Some("car").unwrap_or("bike"), "car"); |
| 1029 | /// assert_eq!(None.unwrap_or("bike"), "bike"); |
| 1030 | /// ``` |
| 1031 | #[inline] |
| 1032 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1033 | #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 1034 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1035 | pub const fn unwrap_or(self, default: T) -> T |
| 1036 | where |
| 1037 | T: [const] Destruct, |
| 1038 | { |
| 1039 | match self { |
| 1040 | Some(x) => x, |
| 1041 | None => default, |
| 1042 | } |
| 1043 | } |
| 1044 | |
| 1045 | /// Returns the contained [`Some`] value or computes it from a closure. |
| 1046 | /// |
| 1047 | /// # Examples |
| 1048 | /// |
| 1049 | /// ``` |
| 1050 | /// let k = 10; |
| 1051 | /// assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4); |
| 1052 | /// assert_eq!(None.unwrap_or_else(|| 2 * k), 20); |
| 1053 | /// ``` |
| 1054 | #[inline] |
| 1055 | #[track_caller] |
| 1056 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1057 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1058 | pub const fn unwrap_or_else<F>(self, f: F) -> T |
| 1059 | where |
| 1060 | F: [const] FnOnce() -> T + [const] Destruct, |
| 1061 | { |
| 1062 | match self { |
| 1063 | Some(x) => x, |
| 1064 | None => f(), |
| 1065 | } |
| 1066 | } |
| 1067 | |
| 1068 | /// Returns the contained [`Some`] value or a default. |
| 1069 | /// |
| 1070 | /// Consumes the `self` argument then, if [`Some`], returns the contained |
| 1071 | /// value, otherwise if [`None`], returns the [default value] for that |
| 1072 | /// type. |
| 1073 | /// |
| 1074 | /// # Examples |
| 1075 | /// |
| 1076 | /// ``` |
| 1077 | /// let x: Option<u32> = None; |
| 1078 | /// let y: Option<u32> = Some(12); |
| 1079 | /// |
| 1080 | /// assert_eq!(x.unwrap_or_default(), 0); |
| 1081 | /// assert_eq!(y.unwrap_or_default(), 12); |
| 1082 | /// ``` |
| 1083 | /// |
| 1084 | /// [default value]: Default::default |
| 1085 | /// [`parse`]: str::parse |
| 1086 | /// [`FromStr`]: crate::str::FromStr |
| 1087 | #[inline] |
| 1088 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1089 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1090 | pub const fn unwrap_or_default(self) -> T |
| 1091 | where |
| 1092 | T: [const] Default, |
| 1093 | { |
| 1094 | match self { |
| 1095 | Some(x) => x, |
| 1096 | None => T::default(), |
| 1097 | } |
| 1098 | } |
| 1099 | |
| 1100 | /// Returns the contained [`Some`] value, consuming the `self` value, |
| 1101 | /// without checking that the value is not [`None`]. |
| 1102 | /// |
| 1103 | /// # Safety |
| 1104 | /// |
| 1105 | /// Calling this method on [`None`] is *[undefined behavior]*. |
| 1106 | /// |
| 1107 | /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html |
| 1108 | /// |
| 1109 | /// # Examples |
| 1110 | /// |
| 1111 | /// ``` |
| 1112 | /// let x = Some("air"); |
| 1113 | /// assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); |
| 1114 | /// ``` |
| 1115 | /// |
| 1116 | /// ```no_run |
| 1117 | /// let x: Option<&str> = None; |
| 1118 | /// assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior! |
| 1119 | /// ``` |
| 1120 | #[inline] |
| 1121 | #[track_caller] |
| 1122 | #[stable(feature = "option_result_unwrap_unchecked", since = "1.58.0")] |
| 1123 | #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 1124 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 1125 | pub const unsafe fn unwrap_unchecked(self) -> T { |
| 1126 | match self { |
| 1127 | Some(val) => val, |
| 1128 | // SAFETY: the safety contract must be upheld by the caller. |
| 1129 | None => unsafe { hint::unreachable_unchecked() }, |
| 1130 | } |
| 1131 | } |
| 1132 | |
| 1133 | ///////////////////////////////////////////////////////////////////////// |
| 1134 | // Transforming contained values |
| 1135 | ///////////////////////////////////////////////////////////////////////// |
| 1136 | |
| 1137 | /// Maps an `Option<T>` to `Option<U>` by applying a function to a contained value (if `Some`) or returns `None` (if `None`). |
| 1138 | /// |
| 1139 | /// # Examples |
| 1140 | /// |
| 1141 | /// Calculates the length of an <code>Option<[String]></code> as an |
| 1142 | /// <code>Option<[usize]></code>, consuming the original: |
| 1143 | /// |
| 1144 | /// [String]: ../../std/string/struct.String.html "String" |
| 1145 | /// ``` |
| 1146 | /// let maybe_some_string = Some(String::from("Hello, World!")); |
| 1147 | /// // `Option::map` takes self *by value*, consuming `maybe_some_string` |
| 1148 | /// let maybe_some_len = maybe_some_string.map(|s| s.len()); |
| 1149 | /// assert_eq!(maybe_some_len, Some(13)); |
| 1150 | /// |
| 1151 | /// let x: Option<&str> = None; |
| 1152 | /// assert_eq!(x.map(|s| s.len()), None); |
| 1153 | /// ``` |
| 1154 | #[inline] |
| 1155 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1156 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1157 | pub const fn map<U, F>(self, f: F) -> Option<U> |
| 1158 | where |
| 1159 | F: [const] FnOnce(T) -> U + [const] Destruct, |
| 1160 | { |
| 1161 | match self { |
| 1162 | Some(x) => Some(f(x)), |
| 1163 | None => None, |
| 1164 | } |
| 1165 | } |
| 1166 | |
| 1167 | /// Calls a function with a reference to the contained value if [`Some`]. |
| 1168 | /// |
| 1169 | /// Returns the original option. |
| 1170 | /// |
| 1171 | /// # Examples |
| 1172 | /// |
| 1173 | /// ``` |
| 1174 | /// let list = vec![1, 2, 3]; |
| 1175 | /// |
| 1176 | /// // prints "got: 2" |
| 1177 | /// let x = list |
| 1178 | /// .get(1) |
| 1179 | /// .inspect(|x| println!("got: {x}")) |
| 1180 | /// .expect("list should be long enough"); |
| 1181 | /// |
| 1182 | /// // prints nothing |
| 1183 | /// list.get(5).inspect(|x| println!("got: {x}")); |
| 1184 | /// ``` |
| 1185 | #[inline] |
| 1186 | #[stable(feature = "result_option_inspect", since = "1.76.0")] |
| 1187 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1188 | pub const fn inspect<F>(self, f: F) -> Self |
| 1189 | where |
| 1190 | F: [const] FnOnce(&T) + [const] Destruct, |
| 1191 | { |
| 1192 | if let Some(ref x) = self { |
| 1193 | f(x); |
| 1194 | } |
| 1195 | |
| 1196 | self |
| 1197 | } |
| 1198 | |
| 1199 | /// Returns the provided default result (if none), |
| 1200 | /// or applies a function to the contained value (if any). |
| 1201 | /// |
| 1202 | /// Arguments passed to `map_or` are eagerly evaluated; if you are passing |
| 1203 | /// the result of a function call, it is recommended to use [`map_or_else`], |
| 1204 | /// which is lazily evaluated. |
| 1205 | /// |
| 1206 | /// [`map_or_else`]: Option::map_or_else |
| 1207 | /// |
| 1208 | /// # Examples |
| 1209 | /// |
| 1210 | /// ``` |
| 1211 | /// let x = Some("foo"); |
| 1212 | /// assert_eq!(x.map_or(42, |v| v.len()), 3); |
| 1213 | /// |
| 1214 | /// let x: Option<&str> = None; |
| 1215 | /// assert_eq!(x.map_or(42, |v| v.len()), 42); |
| 1216 | /// ``` |
| 1217 | #[inline] |
| 1218 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1219 | #[must_use = "if you don't need the returned value, use `if let` instead"] |
| 1220 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1221 | pub const fn map_or<U, F>(self, default: U, f: F) -> U |
| 1222 | where |
| 1223 | F: [const] FnOnce(T) -> U + [const] Destruct, |
| 1224 | U: [const] Destruct, |
| 1225 | { |
| 1226 | match self { |
| 1227 | Some(t) => f(t), |
| 1228 | None => default, |
| 1229 | } |
| 1230 | } |
| 1231 | |
| 1232 | /// Computes a default function result (if none), or |
| 1233 | /// applies a different function to the contained value (if any). |
| 1234 | /// |
| 1235 | /// # Basic examples |
| 1236 | /// |
| 1237 | /// ``` |
| 1238 | /// let k = 21; |
| 1239 | /// |
| 1240 | /// let x = Some("foo"); |
| 1241 | /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3); |
| 1242 | /// |
| 1243 | /// let x: Option<&str> = None; |
| 1244 | /// assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42); |
| 1245 | /// ``` |
| 1246 | /// |
| 1247 | /// # Handling a Result-based fallback |
| 1248 | /// |
| 1249 | /// A somewhat common occurrence when dealing with optional values |
| 1250 | /// in combination with [`Result<T, E>`] is the case where one wants to invoke |
| 1251 | /// a fallible fallback if the option is not present. This example |
| 1252 | /// parses a command line argument (if present), or the contents of a file to |
| 1253 | /// an integer. However, unlike accessing the command line argument, reading |
| 1254 | /// the file is fallible, so it must be wrapped with `Ok`. |
| 1255 | /// |
| 1256 | /// ```no_run |
| 1257 | /// # fn main() -> Result<(), Box<dyn std::error::Error>> { |
| 1258 | /// let v: u64 = std::env::args() |
| 1259 | /// .nth(1) |
| 1260 | /// .map_or_else(|| std::fs::read_to_string("/etc/someconfig.conf"), Ok)? |
| 1261 | /// .parse()?; |
| 1262 | /// # Ok(()) |
| 1263 | /// # } |
| 1264 | /// ``` |
| 1265 | #[inline] |
| 1266 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1267 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1268 | pub const fn map_or_else<U, D, F>(self, default: D, f: F) -> U |
| 1269 | where |
| 1270 | D: [const] FnOnce() -> U + [const] Destruct, |
| 1271 | F: [const] FnOnce(T) -> U + [const] Destruct, |
| 1272 | { |
| 1273 | match self { |
| 1274 | Some(t) => f(t), |
| 1275 | None => default(), |
| 1276 | } |
| 1277 | } |
| 1278 | |
| 1279 | /// Maps an `Option<T>` to a `U` by applying function `f` to the contained |
| 1280 | /// value if the option is [`Some`], otherwise if [`None`], returns the |
| 1281 | /// [default value] for the type `U`. |
| 1282 | /// |
| 1283 | /// # Examples |
| 1284 | /// |
| 1285 | /// ``` |
| 1286 | /// #![feature(result_option_map_or_default)] |
| 1287 | /// |
| 1288 | /// let x: Option<&str> = Some("hi"); |
| 1289 | /// let y: Option<&str> = None; |
| 1290 | /// |
| 1291 | /// assert_eq!(x.map_or_default(|x| x.len()), 2); |
| 1292 | /// assert_eq!(y.map_or_default(|y| y.len()), 0); |
| 1293 | /// ``` |
| 1294 | /// |
| 1295 | /// [default value]: Default::default |
| 1296 | #[inline] |
| 1297 | #[unstable(feature = "result_option_map_or_default", issue = "138099")] |
| 1298 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1299 | pub const fn map_or_default<U, F>(self, f: F) -> U |
| 1300 | where |
| 1301 | U: [const] Default, |
| 1302 | F: [const] FnOnce(T) -> U + [const] Destruct, |
| 1303 | { |
| 1304 | match self { |
| 1305 | Some(t) => f(t), |
| 1306 | None => U::default(), |
| 1307 | } |
| 1308 | } |
| 1309 | |
| 1310 | /// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to |
| 1311 | /// [`Ok(v)`] and [`None`] to [`Err(err)`]. |
| 1312 | /// |
| 1313 | /// Arguments passed to `ok_or` are eagerly evaluated; if you are passing the |
| 1314 | /// result of a function call, it is recommended to use [`ok_or_else`], which is |
| 1315 | /// lazily evaluated. |
| 1316 | /// |
| 1317 | /// [`Ok(v)`]: Ok |
| 1318 | /// [`Err(err)`]: Err |
| 1319 | /// [`Some(v)`]: Some |
| 1320 | /// [`ok_or_else`]: Option::ok_or_else |
| 1321 | /// |
| 1322 | /// # Examples |
| 1323 | /// |
| 1324 | /// ``` |
| 1325 | /// let x = Some("foo"); |
| 1326 | /// assert_eq!(x.ok_or(0), Ok("foo")); |
| 1327 | /// |
| 1328 | /// let x: Option<&str> = None; |
| 1329 | /// assert_eq!(x.ok_or(0), Err(0)); |
| 1330 | /// ``` |
| 1331 | #[inline] |
| 1332 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1333 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1334 | pub const fn ok_or<E: [const] Destruct>(self, err: E) -> Result<T, E> { |
| 1335 | match self { |
| 1336 | Some(v) => Ok(v), |
| 1337 | None => Err(err), |
| 1338 | } |
| 1339 | } |
| 1340 | |
| 1341 | /// Transforms the `Option<T>` into a [`Result<T, E>`], mapping [`Some(v)`] to |
| 1342 | /// [`Ok(v)`] and [`None`] to [`Err(err())`]. |
| 1343 | /// |
| 1344 | /// [`Ok(v)`]: Ok |
| 1345 | /// [`Err(err())`]: Err |
| 1346 | /// [`Some(v)`]: Some |
| 1347 | /// |
| 1348 | /// # Examples |
| 1349 | /// |
| 1350 | /// ``` |
| 1351 | /// let x = Some("foo"); |
| 1352 | /// assert_eq!(x.ok_or_else(|| 0), Ok("foo")); |
| 1353 | /// |
| 1354 | /// let x: Option<&str> = None; |
| 1355 | /// assert_eq!(x.ok_or_else(|| 0), Err(0)); |
| 1356 | /// ``` |
| 1357 | #[inline] |
| 1358 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1359 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1360 | pub const fn ok_or_else<E, F>(self, err: F) -> Result<T, E> |
| 1361 | where |
| 1362 | F: [const] FnOnce() -> E + [const] Destruct, |
| 1363 | { |
| 1364 | match self { |
| 1365 | Some(v) => Ok(v), |
| 1366 | None => Err(err()), |
| 1367 | } |
| 1368 | } |
| 1369 | |
| 1370 | /// Converts from `Option<T>` (or `&Option<T>`) to `Option<&T::Target>`. |
| 1371 | /// |
| 1372 | /// Leaves the original Option in-place, creating a new one with a reference |
| 1373 | /// to the original one, additionally coercing the contents via [`Deref`]. |
| 1374 | /// |
| 1375 | /// # Examples |
| 1376 | /// |
| 1377 | /// ``` |
| 1378 | /// let x: Option<String> = Some("hey".to_owned()); |
| 1379 | /// assert_eq!(x.as_deref(), Some("hey")); |
| 1380 | /// |
| 1381 | /// let x: Option<String> = None; |
| 1382 | /// assert_eq!(x.as_deref(), None); |
| 1383 | /// ``` |
| 1384 | #[inline] |
| 1385 | #[stable(feature = "option_deref", since = "1.40.0")] |
| 1386 | #[rustc_const_unstable(feature = "const_convert", issue = "143773")] |
| 1387 | pub const fn as_deref(&self) -> Option<&T::Target> |
| 1388 | where |
| 1389 | T: [const] Deref, |
| 1390 | { |
| 1391 | self.as_ref().map(Deref::deref) |
| 1392 | } |
| 1393 | |
| 1394 | /// Converts from `Option<T>` (or `&mut Option<T>`) to `Option<&mut T::Target>`. |
| 1395 | /// |
| 1396 | /// Leaves the original `Option` in-place, creating a new one containing a mutable reference to |
| 1397 | /// the inner type's [`Deref::Target`] type. |
| 1398 | /// |
| 1399 | /// # Examples |
| 1400 | /// |
| 1401 | /// ``` |
| 1402 | /// let mut x: Option<String> = Some("hey".to_owned()); |
| 1403 | /// assert_eq!(x.as_deref_mut().map(|x| { |
| 1404 | /// x.make_ascii_uppercase(); |
| 1405 | /// x |
| 1406 | /// }), Some("HEY".to_owned().as_mut_str())); |
| 1407 | /// ``` |
| 1408 | #[inline] |
| 1409 | #[stable(feature = "option_deref", since = "1.40.0")] |
| 1410 | #[rustc_const_unstable(feature = "const_convert", issue = "143773")] |
| 1411 | pub const fn as_deref_mut(&mut self) -> Option<&mut T::Target> |
| 1412 | where |
| 1413 | T: [const] DerefMut, |
| 1414 | { |
| 1415 | self.as_mut().map(DerefMut::deref_mut) |
| 1416 | } |
| 1417 | |
| 1418 | ///////////////////////////////////////////////////////////////////////// |
| 1419 | // Iterator constructors |
| 1420 | ///////////////////////////////////////////////////////////////////////// |
| 1421 | |
| 1422 | /// Returns an iterator over the possibly contained value. |
| 1423 | /// |
| 1424 | /// # Examples |
| 1425 | /// |
| 1426 | /// ``` |
| 1427 | /// let x = Some(4); |
| 1428 | /// assert_eq!(x.iter().next(), Some(&4)); |
| 1429 | /// |
| 1430 | /// let x: Option<u32> = None; |
| 1431 | /// assert_eq!(x.iter().next(), None); |
| 1432 | /// ``` |
| 1433 | #[inline] |
| 1434 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1435 | pub fn iter(&self) -> Iter<'_, T> { |
| 1436 | Iter { inner: Item { opt: self.as_ref() } } |
| 1437 | } |
| 1438 | |
| 1439 | /// Returns a mutable iterator over the possibly contained value. |
| 1440 | /// |
| 1441 | /// # Examples |
| 1442 | /// |
| 1443 | /// ``` |
| 1444 | /// let mut x = Some(4); |
| 1445 | /// match x.iter_mut().next() { |
| 1446 | /// Some(v) => *v = 42, |
| 1447 | /// None => {}, |
| 1448 | /// } |
| 1449 | /// assert_eq!(x, Some(42)); |
| 1450 | /// |
| 1451 | /// let mut x: Option<u32> = None; |
| 1452 | /// assert_eq!(x.iter_mut().next(), None); |
| 1453 | /// ``` |
| 1454 | #[inline] |
| 1455 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1456 | pub fn iter_mut(&mut self) -> IterMut<'_, T> { |
| 1457 | IterMut { inner: Item { opt: self.as_mut() } } |
| 1458 | } |
| 1459 | |
| 1460 | ///////////////////////////////////////////////////////////////////////// |
| 1461 | // Boolean operations on the values, eager and lazy |
| 1462 | ///////////////////////////////////////////////////////////////////////// |
| 1463 | |
| 1464 | /// Returns [`None`] if the option is [`None`], otherwise returns `optb`. |
| 1465 | /// |
| 1466 | /// Arguments passed to `and` are eagerly evaluated; if you are passing the |
| 1467 | /// result of a function call, it is recommended to use [`and_then`], which is |
| 1468 | /// lazily evaluated. |
| 1469 | /// |
| 1470 | /// [`and_then`]: Option::and_then |
| 1471 | /// |
| 1472 | /// # Examples |
| 1473 | /// |
| 1474 | /// ``` |
| 1475 | /// let x = Some(2); |
| 1476 | /// let y: Option<&str> = None; |
| 1477 | /// assert_eq!(x.and(y), None); |
| 1478 | /// |
| 1479 | /// let x: Option<u32> = None; |
| 1480 | /// let y = Some("foo"); |
| 1481 | /// assert_eq!(x.and(y), None); |
| 1482 | /// |
| 1483 | /// let x = Some(2); |
| 1484 | /// let y = Some("foo"); |
| 1485 | /// assert_eq!(x.and(y), Some("foo")); |
| 1486 | /// |
| 1487 | /// let x: Option<u32> = None; |
| 1488 | /// let y: Option<&str> = None; |
| 1489 | /// assert_eq!(x.and(y), None); |
| 1490 | /// ``` |
| 1491 | #[inline] |
| 1492 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1493 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1494 | pub const fn and<U>(self, optb: Option<U>) -> Option<U> |
| 1495 | where |
| 1496 | T: [const] Destruct, |
| 1497 | U: [const] Destruct, |
| 1498 | { |
| 1499 | match self { |
| 1500 | Some(_) => optb, |
| 1501 | None => None, |
| 1502 | } |
| 1503 | } |
| 1504 | |
| 1505 | /// Returns [`None`] if the option is [`None`], otherwise calls `f` with the |
| 1506 | /// wrapped value and returns the result. |
| 1507 | /// |
| 1508 | /// Some languages call this operation flatmap. |
| 1509 | /// |
| 1510 | /// # Examples |
| 1511 | /// |
| 1512 | /// ``` |
| 1513 | /// fn sq_then_to_string(x: u32) -> Option<String> { |
| 1514 | /// x.checked_mul(x).map(|sq| sq.to_string()) |
| 1515 | /// } |
| 1516 | /// |
| 1517 | /// assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string())); |
| 1518 | /// assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed! |
| 1519 | /// assert_eq!(None.and_then(sq_then_to_string), None); |
| 1520 | /// ``` |
| 1521 | /// |
| 1522 | /// Often used to chain fallible operations that may return [`None`]. |
| 1523 | /// |
| 1524 | /// ``` |
| 1525 | /// let arr_2d = [["A0", "A1"], ["B0", "B1"]]; |
| 1526 | /// |
| 1527 | /// let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1)); |
| 1528 | /// assert_eq!(item_0_1, Some(&"A1")); |
| 1529 | /// |
| 1530 | /// let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0)); |
| 1531 | /// assert_eq!(item_2_0, None); |
| 1532 | /// ``` |
| 1533 | #[doc(alias = "flatmap")] |
| 1534 | #[inline] |
| 1535 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1536 | #[rustc_confusables("flat_map", "flatmap")] |
| 1537 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1538 | pub const fn and_then<U, F>(self, f: F) -> Option<U> |
| 1539 | where |
| 1540 | F: [const] FnOnce(T) -> Option<U> + [const] Destruct, |
| 1541 | { |
| 1542 | match self { |
| 1543 | Some(x) => f(x), |
| 1544 | None => None, |
| 1545 | } |
| 1546 | } |
| 1547 | |
| 1548 | /// Returns [`None`] if the option is [`None`], otherwise calls `predicate` |
| 1549 | /// with the wrapped value and returns: |
| 1550 | /// |
| 1551 | /// - [`Some(t)`] if `predicate` returns `true` (where `t` is the wrapped |
| 1552 | /// value), and |
| 1553 | /// - [`None`] if `predicate` returns `false`. |
| 1554 | /// |
| 1555 | /// This function works similar to [`Iterator::filter()`]. You can imagine |
| 1556 | /// the `Option<T>` being an iterator over one or zero elements. `filter()` |
| 1557 | /// lets you decide which elements to keep. |
| 1558 | /// |
| 1559 | /// # Examples |
| 1560 | /// |
| 1561 | /// ```rust |
| 1562 | /// fn is_even(n: &i32) -> bool { |
| 1563 | /// n % 2 == 0 |
| 1564 | /// } |
| 1565 | /// |
| 1566 | /// assert_eq!(None.filter(is_even), None); |
| 1567 | /// assert_eq!(Some(3).filter(is_even), None); |
| 1568 | /// assert_eq!(Some(4).filter(is_even), Some(4)); |
| 1569 | /// ``` |
| 1570 | /// |
| 1571 | /// [`Some(t)`]: Some |
| 1572 | #[inline] |
| 1573 | #[stable(feature = "option_filter", since = "1.27.0")] |
| 1574 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1575 | pub const fn filter<P>(self, predicate: P) -> Self |
| 1576 | where |
| 1577 | P: [const] FnOnce(&T) -> bool + [const] Destruct, |
| 1578 | T: [const] Destruct, |
| 1579 | { |
| 1580 | if let Some(x) = self { |
| 1581 | if predicate(&x) { |
| 1582 | return Some(x); |
| 1583 | } |
| 1584 | } |
| 1585 | None |
| 1586 | } |
| 1587 | |
| 1588 | /// Returns the option if it contains a value, otherwise returns `optb`. |
| 1589 | /// |
| 1590 | /// Arguments passed to `or` are eagerly evaluated; if you are passing the |
| 1591 | /// result of a function call, it is recommended to use [`or_else`], which is |
| 1592 | /// lazily evaluated. |
| 1593 | /// |
| 1594 | /// [`or_else`]: Option::or_else |
| 1595 | /// |
| 1596 | /// # Examples |
| 1597 | /// |
| 1598 | /// ``` |
| 1599 | /// let x = Some(2); |
| 1600 | /// let y = None; |
| 1601 | /// assert_eq!(x.or(y), Some(2)); |
| 1602 | /// |
| 1603 | /// let x = None; |
| 1604 | /// let y = Some(100); |
| 1605 | /// assert_eq!(x.or(y), Some(100)); |
| 1606 | /// |
| 1607 | /// let x = Some(2); |
| 1608 | /// let y = Some(100); |
| 1609 | /// assert_eq!(x.or(y), Some(2)); |
| 1610 | /// |
| 1611 | /// let x: Option<u32> = None; |
| 1612 | /// let y = None; |
| 1613 | /// assert_eq!(x.or(y), None); |
| 1614 | /// ``` |
| 1615 | #[inline] |
| 1616 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1617 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1618 | pub const fn or(self, optb: Option<T>) -> Option<T> |
| 1619 | where |
| 1620 | T: [const] Destruct, |
| 1621 | { |
| 1622 | match self { |
| 1623 | x @ Some(_) => x, |
| 1624 | None => optb, |
| 1625 | } |
| 1626 | } |
| 1627 | |
| 1628 | /// Returns the option if it contains a value, otherwise calls `f` and |
| 1629 | /// returns the result. |
| 1630 | /// |
| 1631 | /// # Examples |
| 1632 | /// |
| 1633 | /// ``` |
| 1634 | /// fn nobody() -> Option<&'static str> { None } |
| 1635 | /// fn vikings() -> Option<&'static str> { Some("vikings") } |
| 1636 | /// |
| 1637 | /// assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians")); |
| 1638 | /// assert_eq!(None.or_else(vikings), Some("vikings")); |
| 1639 | /// assert_eq!(None.or_else(nobody), None); |
| 1640 | /// ``` |
| 1641 | #[inline] |
| 1642 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1643 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1644 | pub const fn or_else<F>(self, f: F) -> Option<T> |
| 1645 | where |
| 1646 | F: [const] FnOnce() -> Option<T> + [const] Destruct, |
| 1647 | //FIXME(const_hack): this `T: [const] Destruct` is unnecessary, but even precise live drops can't tell |
| 1648 | // no value of type `T` gets dropped here |
| 1649 | T: [const] Destruct, |
| 1650 | { |
| 1651 | match self { |
| 1652 | x @ Some(_) => x, |
| 1653 | None => f(), |
| 1654 | } |
| 1655 | } |
| 1656 | |
| 1657 | /// Returns [`Some`] if exactly one of `self`, `optb` is [`Some`], otherwise returns [`None`]. |
| 1658 | /// |
| 1659 | /// # Examples |
| 1660 | /// |
| 1661 | /// ``` |
| 1662 | /// let x = Some(2); |
| 1663 | /// let y: Option<u32> = None; |
| 1664 | /// assert_eq!(x.xor(y), Some(2)); |
| 1665 | /// |
| 1666 | /// let x: Option<u32> = None; |
| 1667 | /// let y = Some(2); |
| 1668 | /// assert_eq!(x.xor(y), Some(2)); |
| 1669 | /// |
| 1670 | /// let x = Some(2); |
| 1671 | /// let y = Some(2); |
| 1672 | /// assert_eq!(x.xor(y), None); |
| 1673 | /// |
| 1674 | /// let x: Option<u32> = None; |
| 1675 | /// let y: Option<u32> = None; |
| 1676 | /// assert_eq!(x.xor(y), None); |
| 1677 | /// ``` |
| 1678 | #[inline] |
| 1679 | #[stable(feature = "option_xor", since = "1.37.0")] |
| 1680 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1681 | pub const fn xor(self, optb: Option<T>) -> Option<T> |
| 1682 | where |
| 1683 | T: [const] Destruct, |
| 1684 | { |
| 1685 | match (self, optb) { |
| 1686 | (a @ Some(_), None) => a, |
| 1687 | (None, b @ Some(_)) => b, |
| 1688 | _ => None, |
| 1689 | } |
| 1690 | } |
| 1691 | |
| 1692 | ///////////////////////////////////////////////////////////////////////// |
| 1693 | // Entry-like operations to insert a value and return a reference |
| 1694 | ///////////////////////////////////////////////////////////////////////// |
| 1695 | |
| 1696 | /// Inserts `value` into the option, then returns a mutable reference to it. |
| 1697 | /// |
| 1698 | /// If the option already contains a value, the old value is dropped. |
| 1699 | /// |
| 1700 | /// See also [`Option::get_or_insert`], which doesn't update the value if |
| 1701 | /// the option already contains [`Some`]. |
| 1702 | /// |
| 1703 | /// # Example |
| 1704 | /// |
| 1705 | /// ``` |
| 1706 | /// let mut opt = None; |
| 1707 | /// let val = opt.insert(1); |
| 1708 | /// assert_eq!(*val, 1); |
| 1709 | /// assert_eq!(opt.unwrap(), 1); |
| 1710 | /// let val = opt.insert(2); |
| 1711 | /// assert_eq!(*val, 2); |
| 1712 | /// *val = 3; |
| 1713 | /// assert_eq!(opt.unwrap(), 3); |
| 1714 | /// ``` |
| 1715 | #[must_use = "if you intended to set a value, consider assignment instead"] |
| 1716 | #[inline] |
| 1717 | #[stable(feature = "option_insert", since = "1.53.0")] |
| 1718 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1719 | pub const fn insert(&mut self, value: T) -> &mut T |
| 1720 | where |
| 1721 | T: [const] Destruct, |
| 1722 | { |
| 1723 | *self = Some(value); |
| 1724 | |
| 1725 | // SAFETY: the code above just filled the option |
| 1726 | unsafe { self.as_mut().unwrap_unchecked() } |
| 1727 | } |
| 1728 | |
| 1729 | /// Inserts `value` into the option if it is [`None`], then |
| 1730 | /// returns a mutable reference to the contained value. |
| 1731 | /// |
| 1732 | /// See also [`Option::insert`], which updates the value even if |
| 1733 | /// the option already contains [`Some`]. |
| 1734 | /// |
| 1735 | /// # Examples |
| 1736 | /// |
| 1737 | /// ``` |
| 1738 | /// let mut x = None; |
| 1739 | /// |
| 1740 | /// { |
| 1741 | /// let y: &mut u32 = x.get_or_insert(5); |
| 1742 | /// assert_eq!(y, &5); |
| 1743 | /// |
| 1744 | /// *y = 7; |
| 1745 | /// } |
| 1746 | /// |
| 1747 | /// assert_eq!(x, Some(7)); |
| 1748 | /// ``` |
| 1749 | #[inline] |
| 1750 | #[stable(feature = "option_entry", since = "1.20.0")] |
| 1751 | pub fn get_or_insert(&mut self, value: T) -> &mut T { |
| 1752 | self.get_or_insert_with(|| value) |
| 1753 | } |
| 1754 | |
| 1755 | /// Inserts the default value into the option if it is [`None`], then |
| 1756 | /// returns a mutable reference to the contained value. |
| 1757 | /// |
| 1758 | /// # Examples |
| 1759 | /// |
| 1760 | /// ``` |
| 1761 | /// let mut x = None; |
| 1762 | /// |
| 1763 | /// { |
| 1764 | /// let y: &mut u32 = x.get_or_insert_default(); |
| 1765 | /// assert_eq!(y, &0); |
| 1766 | /// |
| 1767 | /// *y = 7; |
| 1768 | /// } |
| 1769 | /// |
| 1770 | /// assert_eq!(x, Some(7)); |
| 1771 | /// ``` |
| 1772 | #[inline] |
| 1773 | #[stable(feature = "option_get_or_insert_default", since = "1.83.0")] |
| 1774 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1775 | pub const fn get_or_insert_default(&mut self) -> &mut T |
| 1776 | where |
| 1777 | T: [const] Default, |
| 1778 | { |
| 1779 | self.get_or_insert_with(T::default) |
| 1780 | } |
| 1781 | |
| 1782 | /// Inserts a value computed from `f` into the option if it is [`None`], |
| 1783 | /// then returns a mutable reference to the contained value. |
| 1784 | /// |
| 1785 | /// # Examples |
| 1786 | /// |
| 1787 | /// ``` |
| 1788 | /// let mut x = None; |
| 1789 | /// |
| 1790 | /// { |
| 1791 | /// let y: &mut u32 = x.get_or_insert_with(|| 5); |
| 1792 | /// assert_eq!(y, &5); |
| 1793 | /// |
| 1794 | /// *y = 7; |
| 1795 | /// } |
| 1796 | /// |
| 1797 | /// assert_eq!(x, Some(7)); |
| 1798 | /// ``` |
| 1799 | #[inline] |
| 1800 | #[stable(feature = "option_entry", since = "1.20.0")] |
| 1801 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1802 | pub const fn get_or_insert_with<F>(&mut self, f: F) -> &mut T |
| 1803 | where |
| 1804 | F: [const] FnOnce() -> T + [const] Destruct, |
| 1805 | { |
| 1806 | if let None = self { |
| 1807 | // The effect of the following statement is identical to |
| 1808 | // *self = Some(f()); |
| 1809 | // except that it does not drop the old value of `*self`. This is not a leak, because |
| 1810 | // we just checked that the old value is `None`, which contains no fields to drop. |
| 1811 | // This implementation strategy |
| 1812 | // |
| 1813 | // * avoids needing a `T: [const] Destruct` bound, to the benefit of `const` callers, |
| 1814 | // * and avoids possibly compiling needless drop code (as would sometimes happen in the |
| 1815 | // previous implementation), to the benefit of non-`const` callers. |
| 1816 | // |
| 1817 | // FIXME(const-hack): It would be nice if this weird trick were made obsolete |
| 1818 | // (though that is likely to be hard/wontfix). |
| 1819 | // |
| 1820 | // It could also be expressed as `unsafe { core::ptr::write(self, Some(f())) }`, but |
| 1821 | // no reason is currently known to use additional unsafe code here. |
| 1822 | |
| 1823 | mem::forget(mem::replace(self, Some(f()))); |
| 1824 | } |
| 1825 | |
| 1826 | // SAFETY: a `None` variant for `self` would have been replaced by a `Some` |
| 1827 | // variant in the code above. |
| 1828 | unsafe { self.as_mut().unwrap_unchecked() } |
| 1829 | } |
| 1830 | |
| 1831 | /// If the option is `None`, calls the closure and inserts its output if successful. |
| 1832 | /// |
| 1833 | /// If the closure returns a residual value such as `Err` or `None`, |
| 1834 | /// that residual value is returned and nothing is inserted. |
| 1835 | /// |
| 1836 | /// If the option is `Some`, nothing is inserted. |
| 1837 | /// |
| 1838 | /// Unless a residual is returned, a mutable reference to the value |
| 1839 | /// of the option will be output. |
| 1840 | /// |
| 1841 | /// # Examples |
| 1842 | /// |
| 1843 | /// ``` |
| 1844 | /// #![feature(option_get_or_try_insert_with)] |
| 1845 | /// let mut o1: Option<u32> = None; |
| 1846 | /// let mut o2: Option<u8> = None; |
| 1847 | /// |
| 1848 | /// let number = "12345"; |
| 1849 | /// |
| 1850 | /// assert_eq!(o1.get_or_try_insert_with(|| number.parse()).copied(), Ok(12345)); |
| 1851 | /// assert!(o2.get_or_try_insert_with(|| number.parse()).is_err()); |
| 1852 | /// assert_eq!(o1, Some(12345)); |
| 1853 | /// assert_eq!(o2, None); |
| 1854 | /// ``` |
| 1855 | #[inline] |
| 1856 | #[unstable(feature = "option_get_or_try_insert_with", issue = "143648")] |
| 1857 | pub fn get_or_try_insert_with<'a, R, F>( |
| 1858 | &'a mut self, |
| 1859 | f: F, |
| 1860 | ) -> <R::Residual as Residual<&'a mut T>>::TryType |
| 1861 | where |
| 1862 | F: FnOnce() -> R, |
| 1863 | R: Try<Output = T, Residual: Residual<&'a mut T>>, |
| 1864 | { |
| 1865 | if let None = self { |
| 1866 | *self = Some(f()?); |
| 1867 | } |
| 1868 | // SAFETY: a `None` variant for `self` would have been replaced by a `Some` |
| 1869 | // variant in the code above. |
| 1870 | |
| 1871 | Try::from_output(unsafe { self.as_mut().unwrap_unchecked() }) |
| 1872 | } |
| 1873 | |
| 1874 | ///////////////////////////////////////////////////////////////////////// |
| 1875 | // Misc |
| 1876 | ///////////////////////////////////////////////////////////////////////// |
| 1877 | |
| 1878 | /// Takes the value out of the option, leaving a [`None`] in its place. |
| 1879 | /// |
| 1880 | /// # Examples |
| 1881 | /// |
| 1882 | /// ``` |
| 1883 | /// let mut x = Some(2); |
| 1884 | /// let y = x.take(); |
| 1885 | /// assert_eq!(x, None); |
| 1886 | /// assert_eq!(y, Some(2)); |
| 1887 | /// |
| 1888 | /// let mut x: Option<u32> = None; |
| 1889 | /// let y = x.take(); |
| 1890 | /// assert_eq!(x, None); |
| 1891 | /// assert_eq!(y, None); |
| 1892 | /// ``` |
| 1893 | #[inline] |
| 1894 | #[stable(feature = "rust1", since = "1.0.0")] |
| 1895 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 1896 | pub const fn take(&mut self) -> Option<T> { |
| 1897 | // FIXME(const-hack) replace `mem::replace` by `mem::take` when the latter is const ready |
| 1898 | mem::replace(self, None) |
| 1899 | } |
| 1900 | |
| 1901 | /// Takes the value out of the option, but only if the predicate evaluates to |
| 1902 | /// `true` on a mutable reference to the value. |
| 1903 | /// |
| 1904 | /// In other words, replaces `self` with `None` if the predicate returns `true`. |
| 1905 | /// This method operates similar to [`Option::take`] but conditional. |
| 1906 | /// |
| 1907 | /// # Examples |
| 1908 | /// |
| 1909 | /// ``` |
| 1910 | /// let mut x = Some(42); |
| 1911 | /// |
| 1912 | /// let prev = x.take_if(|v| if *v == 42 { |
| 1913 | /// *v += 1; |
| 1914 | /// false |
| 1915 | /// } else { |
| 1916 | /// false |
| 1917 | /// }); |
| 1918 | /// assert_eq!(x, Some(43)); |
| 1919 | /// assert_eq!(prev, None); |
| 1920 | /// |
| 1921 | /// let prev = x.take_if(|v| *v == 43); |
| 1922 | /// assert_eq!(x, None); |
| 1923 | /// assert_eq!(prev, Some(43)); |
| 1924 | /// ``` |
| 1925 | #[inline] |
| 1926 | #[stable(feature = "option_take_if", since = "1.80.0")] |
| 1927 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1928 | pub const fn take_if<P>(&mut self, predicate: P) -> Option<T> |
| 1929 | where |
| 1930 | P: [const] FnOnce(&mut T) -> bool + [const] Destruct, |
| 1931 | { |
| 1932 | if self.as_mut().map_or(false, predicate) { self.take() } else { None } |
| 1933 | } |
| 1934 | |
| 1935 | /// Replaces the actual value in the option by the value given in parameter, |
| 1936 | /// returning the old value if present, |
| 1937 | /// leaving a [`Some`] in its place without deinitializing either one. |
| 1938 | /// |
| 1939 | /// # Examples |
| 1940 | /// |
| 1941 | /// ``` |
| 1942 | /// let mut x = Some(2); |
| 1943 | /// let old = x.replace(5); |
| 1944 | /// assert_eq!(x, Some(5)); |
| 1945 | /// assert_eq!(old, Some(2)); |
| 1946 | /// |
| 1947 | /// let mut x = None; |
| 1948 | /// let old = x.replace(3); |
| 1949 | /// assert_eq!(x, Some(3)); |
| 1950 | /// assert_eq!(old, None); |
| 1951 | /// ``` |
| 1952 | #[inline] |
| 1953 | #[stable(feature = "option_replace", since = "1.31.0")] |
| 1954 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 1955 | pub const fn replace(&mut self, value: T) -> Option<T> { |
| 1956 | mem::replace(self, Some(value)) |
| 1957 | } |
| 1958 | |
| 1959 | /// Zips `self` with another `Option`. |
| 1960 | /// |
| 1961 | /// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some((s, o))`. |
| 1962 | /// Otherwise, `None` is returned. |
| 1963 | /// |
| 1964 | /// # Examples |
| 1965 | /// |
| 1966 | /// ``` |
| 1967 | /// let x = Some(1); |
| 1968 | /// let y = Some("hi"); |
| 1969 | /// let z = None::<u8>; |
| 1970 | /// |
| 1971 | /// assert_eq!(x.zip(y), Some((1, "hi"))); |
| 1972 | /// assert_eq!(x.zip(z), None); |
| 1973 | /// ``` |
| 1974 | #[stable(feature = "option_zip_option", since = "1.46.0")] |
| 1975 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 1976 | pub const fn zip<U>(self, other: Option<U>) -> Option<(T, U)> |
| 1977 | where |
| 1978 | T: [const] Destruct, |
| 1979 | U: [const] Destruct, |
| 1980 | { |
| 1981 | match (self, other) { |
| 1982 | (Some(a), Some(b)) => Some((a, b)), |
| 1983 | _ => None, |
| 1984 | } |
| 1985 | } |
| 1986 | |
| 1987 | /// Zips `self` and another `Option` with function `f`. |
| 1988 | /// |
| 1989 | /// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some(f(s, o))`. |
| 1990 | /// Otherwise, `None` is returned. |
| 1991 | /// |
| 1992 | /// # Examples |
| 1993 | /// |
| 1994 | /// ``` |
| 1995 | /// #![feature(option_zip)] |
| 1996 | /// |
| 1997 | /// #[derive(Debug, PartialEq)] |
| 1998 | /// struct Point { |
| 1999 | /// x: f64, |
| 2000 | /// y: f64, |
| 2001 | /// } |
| 2002 | /// |
| 2003 | /// impl Point { |
| 2004 | /// fn new(x: f64, y: f64) -> Self { |
| 2005 | /// Self { x, y } |
| 2006 | /// } |
| 2007 | /// } |
| 2008 | /// |
| 2009 | /// let x = Some(17.5); |
| 2010 | /// let y = Some(42.7); |
| 2011 | /// |
| 2012 | /// assert_eq!(x.zip_with(y, Point::new), Some(Point { x: 17.5, y: 42.7 })); |
| 2013 | /// assert_eq!(x.zip_with(None, Point::new), None); |
| 2014 | /// ``` |
| 2015 | #[unstable(feature = "option_zip", issue = "70086")] |
| 2016 | #[rustc_const_unstable(feature = "const_option_ops", issue = "143956")] |
| 2017 | pub const fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R> |
| 2018 | where |
| 2019 | F: [const] FnOnce(T, U) -> R + [const] Destruct, |
| 2020 | T: [const] Destruct, |
| 2021 | U: [const] Destruct, |
| 2022 | { |
| 2023 | match (self, other) { |
| 2024 | (Some(a), Some(b)) => Some(f(a, b)), |
| 2025 | _ => None, |
| 2026 | } |
| 2027 | } |
| 2028 | |
| 2029 | /// Reduces two options into one, using the provided function if both are `Some`. |
| 2030 | /// |
| 2031 | /// If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some(f(s, o))`. |
| 2032 | /// Otherwise, if only one of `self` and `other` is `Some`, that one is returned. |
| 2033 | /// If both `self` and `other` are `None`, `None` is returned. |
| 2034 | /// |
| 2035 | /// # Examples |
| 2036 | /// |
| 2037 | /// ``` |
| 2038 | /// #![feature(option_reduce)] |
| 2039 | /// |
| 2040 | /// let s12 = Some(12); |
| 2041 | /// let s17 = Some(17); |
| 2042 | /// let n = None; |
| 2043 | /// let f = |a, b| a + b; |
| 2044 | /// |
| 2045 | /// assert_eq!(s12.reduce(s17, f), Some(29)); |
| 2046 | /// assert_eq!(s12.reduce(n, f), Some(12)); |
| 2047 | /// assert_eq!(n.reduce(s17, f), Some(17)); |
| 2048 | /// assert_eq!(n.reduce(n, f), None); |
| 2049 | /// ``` |
| 2050 | #[unstable(feature = "option_reduce", issue = "144273")] |
| 2051 | pub fn reduce<U, R, F>(self, other: Option<U>, f: F) -> Option<R> |
| 2052 | where |
| 2053 | T: Into<R>, |
| 2054 | U: Into<R>, |
| 2055 | F: FnOnce(T, U) -> R, |
| 2056 | { |
| 2057 | match (self, other) { |
| 2058 | (Some(a), Some(b)) => Some(f(a, b)), |
| 2059 | (Some(a), _) => Some(a.into()), |
| 2060 | (_, Some(b)) => Some(b.into()), |
| 2061 | _ => None, |
| 2062 | } |
| 2063 | } |
| 2064 | } |
| 2065 | |
| 2066 | impl<T: IntoIterator> Option<T> { |
| 2067 | /// Transforms an optional iterator into an iterator. |
| 2068 | /// |
| 2069 | /// If `self` is `None`, the resulting iterator is empty. |
| 2070 | /// Otherwise, an iterator is made from the `Some` value and returned. |
| 2071 | /// # Examples |
| 2072 | /// ``` |
| 2073 | /// #![feature(option_into_flat_iter)] |
| 2074 | /// |
| 2075 | /// let o1 = Some([1, 2]); |
| 2076 | /// let o2 = None::<&[usize]>; |
| 2077 | /// |
| 2078 | /// assert_eq!(o1.into_flat_iter().collect::<Vec<_>>(), [1, 2]); |
| 2079 | /// assert_eq!(o2.into_flat_iter().collect::<Vec<_>>(), Vec::<&usize>::new()); |
| 2080 | /// ``` |
| 2081 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2082 | pub fn into_flat_iter<A>(self) -> OptionFlatten<A> |
| 2083 | where |
| 2084 | T: IntoIterator<IntoIter = A>, |
| 2085 | { |
| 2086 | OptionFlatten { iter: self.map(IntoIterator::into_iter) } |
| 2087 | } |
| 2088 | } |
| 2089 | |
| 2090 | impl<T, U> Option<(T, U)> { |
| 2091 | /// Unzips an option containing a tuple of two options. |
| 2092 | /// |
| 2093 | /// If `self` is `Some((a, b))` this method returns `(Some(a), Some(b))`. |
| 2094 | /// Otherwise, `(None, None)` is returned. |
| 2095 | /// |
| 2096 | /// # Examples |
| 2097 | /// |
| 2098 | /// ``` |
| 2099 | /// let x = Some((1, "hi")); |
| 2100 | /// let y = None::<(u8, u32)>; |
| 2101 | /// |
| 2102 | /// assert_eq!(x.unzip(), (Some(1), Some("hi"))); |
| 2103 | /// assert_eq!(y.unzip(), (None, None)); |
| 2104 | /// ``` |
| 2105 | #[inline] |
| 2106 | #[stable(feature = "unzip_option", since = "1.66.0")] |
| 2107 | pub fn unzip(self) -> (Option<T>, Option<U>) { |
| 2108 | match self { |
| 2109 | Some((a, b)) => (Some(a), Some(b)), |
| 2110 | None => (None, None), |
| 2111 | } |
| 2112 | } |
| 2113 | } |
| 2114 | |
| 2115 | impl<T> Option<&T> { |
| 2116 | /// Maps an `Option<&T>` to an `Option<T>` by copying the contents of the |
| 2117 | /// option. |
| 2118 | /// |
| 2119 | /// # Examples |
| 2120 | /// |
| 2121 | /// ``` |
| 2122 | /// let x = 12; |
| 2123 | /// let opt_x = Some(&x); |
| 2124 | /// assert_eq!(opt_x, Some(&12)); |
| 2125 | /// let copied = opt_x.copied(); |
| 2126 | /// assert_eq!(copied, Some(12)); |
| 2127 | /// ``` |
| 2128 | #[must_use = "`self` will be dropped if the result is not used"] |
| 2129 | #[stable(feature = "copied", since = "1.35.0")] |
| 2130 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 2131 | pub const fn copied(self) -> Option<T> |
| 2132 | where |
| 2133 | T: Copy, |
| 2134 | { |
| 2135 | // FIXME(const-hack): this implementation, which sidesteps using `Option::map` since it's not const |
| 2136 | // ready yet, should be reverted when possible to avoid code repetition |
| 2137 | match self { |
| 2138 | Some(&v) => Some(v), |
| 2139 | None => None, |
| 2140 | } |
| 2141 | } |
| 2142 | |
| 2143 | /// Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the |
| 2144 | /// option. |
| 2145 | /// |
| 2146 | /// # Examples |
| 2147 | /// |
| 2148 | /// ``` |
| 2149 | /// let x = 12; |
| 2150 | /// let opt_x = Some(&x); |
| 2151 | /// assert_eq!(opt_x, Some(&12)); |
| 2152 | /// let cloned = opt_x.cloned(); |
| 2153 | /// assert_eq!(cloned, Some(12)); |
| 2154 | /// ``` |
| 2155 | #[must_use = "`self` will be dropped if the result is not used"] |
| 2156 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2157 | pub fn cloned(self) -> Option<T> |
| 2158 | where |
| 2159 | T: Clone, |
| 2160 | { |
| 2161 | self.map(T::clone) |
| 2162 | } |
| 2163 | } |
| 2164 | |
| 2165 | impl<T> Option<&mut T> { |
| 2166 | /// Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the |
| 2167 | /// option. |
| 2168 | /// |
| 2169 | /// # Examples |
| 2170 | /// |
| 2171 | /// ``` |
| 2172 | /// let mut x = 12; |
| 2173 | /// let opt_x = Some(&mut x); |
| 2174 | /// assert_eq!(opt_x, Some(&mut 12)); |
| 2175 | /// let copied = opt_x.copied(); |
| 2176 | /// assert_eq!(copied, Some(12)); |
| 2177 | /// ``` |
| 2178 | #[must_use = "`self` will be dropped if the result is not used"] |
| 2179 | #[stable(feature = "copied", since = "1.35.0")] |
| 2180 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 2181 | pub const fn copied(self) -> Option<T> |
| 2182 | where |
| 2183 | T: Copy, |
| 2184 | { |
| 2185 | match self { |
| 2186 | Some(&mut t) => Some(t), |
| 2187 | None => None, |
| 2188 | } |
| 2189 | } |
| 2190 | |
| 2191 | /// Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the |
| 2192 | /// option. |
| 2193 | /// |
| 2194 | /// # Examples |
| 2195 | /// |
| 2196 | /// ``` |
| 2197 | /// let mut x = 12; |
| 2198 | /// let opt_x = Some(&mut x); |
| 2199 | /// assert_eq!(opt_x, Some(&mut 12)); |
| 2200 | /// let cloned = opt_x.cloned(); |
| 2201 | /// assert_eq!(cloned, Some(12)); |
| 2202 | /// ``` |
| 2203 | #[must_use = "`self` will be dropped if the result is not used"] |
| 2204 | #[stable(since = "1.26.0", feature = "option_ref_mut_cloned")] |
| 2205 | pub fn cloned(self) -> Option<T> |
| 2206 | where |
| 2207 | T: Clone, |
| 2208 | { |
| 2209 | self.as_deref().map(T::clone) |
| 2210 | } |
| 2211 | } |
| 2212 | |
| 2213 | impl<T, E> Option<Result<T, E>> { |
| 2214 | /// Transposes an `Option` of a [`Result`] into a [`Result`] of an `Option`. |
| 2215 | /// |
| 2216 | /// <code>[Some]\([Ok]\(\_))</code> is mapped to <code>[Ok]\([Some]\(\_))</code>, |
| 2217 | /// <code>[Some]\([Err]\(\_))</code> is mapped to <code>[Err]\(\_)</code>, |
| 2218 | /// and [`None`] will be mapped to <code>[Ok]\([None])</code>. |
| 2219 | /// |
| 2220 | /// # Examples |
| 2221 | /// |
| 2222 | /// ``` |
| 2223 | /// #[derive(Debug, Eq, PartialEq)] |
| 2224 | /// struct SomeErr; |
| 2225 | /// |
| 2226 | /// let x: Option<Result<i32, SomeErr>> = Some(Ok(5)); |
| 2227 | /// let y: Result<Option<i32>, SomeErr> = Ok(Some(5)); |
| 2228 | /// assert_eq!(x.transpose(), y); |
| 2229 | /// ``` |
| 2230 | #[inline] |
| 2231 | #[stable(feature = "transpose_result", since = "1.33.0")] |
| 2232 | #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 2233 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 2234 | pub const fn transpose(self) -> Result<Option<T>, E> { |
| 2235 | match self { |
| 2236 | Some(Ok(x)) => Ok(Some(x)), |
| 2237 | Some(Err(e)) => Err(e), |
| 2238 | None => Ok(None), |
| 2239 | } |
| 2240 | } |
| 2241 | } |
| 2242 | |
| 2243 | #[cfg_attr(not(panic = "immediate-abort"), inline(never))] |
| 2244 | #[cfg_attr(panic = "immediate-abort", inline)] |
| 2245 | #[cold] |
| 2246 | #[track_caller] |
| 2247 | const fn unwrap_failed() -> ! { |
| 2248 | panic("called `Option::unwrap()` on a `None` value") |
| 2249 | } |
| 2250 | |
| 2251 | // This is a separate function to reduce the code size of .expect() itself. |
| 2252 | #[cfg_attr(not(panic = "immediate-abort"), inline(never))] |
| 2253 | #[cfg_attr(panic = "immediate-abort", inline)] |
| 2254 | #[cold] |
| 2255 | #[track_caller] |
| 2256 | const fn expect_failed(msg: &str) -> ! { |
| 2257 | panic_display(&msg) |
| 2258 | } |
| 2259 | |
| 2260 | ///////////////////////////////////////////////////////////////////////////// |
| 2261 | // Trait implementations |
| 2262 | ///////////////////////////////////////////////////////////////////////////// |
| 2263 | |
| 2264 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2265 | #[rustc_const_unstable(feature = "const_clone", issue = "142757")] |
| 2266 | impl<T> const Clone for Option<T> |
| 2267 | where |
| 2268 | // FIXME(const_hack): the T: [const] Destruct should be inferred from the Self: [const] Destruct in clone_from. |
| 2269 | // See https://github.com/rust-lang/rust/issues/144207 |
| 2270 | T: [const] Clone + [const] Destruct, |
| 2271 | { |
| 2272 | #[inline] |
| 2273 | fn clone(&self) -> Self { |
| 2274 | match self { |
| 2275 | Some(x) => Some(x.clone()), |
| 2276 | None => None, |
| 2277 | } |
| 2278 | } |
| 2279 | |
| 2280 | #[inline] |
| 2281 | fn clone_from(&mut self, source: &Self) { |
| 2282 | match (self, source) { |
| 2283 | (Some(to), Some(from)) => to.clone_from(from), |
| 2284 | (to, from) => *to = from.clone(), |
| 2285 | } |
| 2286 | } |
| 2287 | } |
| 2288 | |
| 2289 | #[unstable(feature = "ergonomic_clones", issue = "132290")] |
| 2290 | impl<T> crate::clone::UseCloned for Option<T> where T: crate::clone::UseCloned {} |
| 2291 | |
| 2292 | #[doc(hidden)] |
| 2293 | #[unstable(feature = "trivial_clone", issue = "none")] |
| 2294 | #[rustc_const_unstable(feature = "const_clone", issue = "142757")] |
| 2295 | unsafe impl<T> const TrivialClone for Option<T> where T: [const] TrivialClone + [const] Destruct {} |
| 2296 | |
| 2297 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2298 | #[rustc_const_unstable(feature = "const_default", issue = "143894")] |
| 2299 | impl<T> const Default for Option<T> { |
| 2300 | /// Returns [`None`][Option::None]. |
| 2301 | /// |
| 2302 | /// # Examples |
| 2303 | /// |
| 2304 | /// ``` |
| 2305 | /// let opt: Option<u32> = Option::default(); |
| 2306 | /// assert!(opt.is_none()); |
| 2307 | /// ``` |
| 2308 | #[inline] |
| 2309 | fn default() -> Option<T> { |
| 2310 | None |
| 2311 | } |
| 2312 | } |
| 2313 | |
| 2314 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2315 | #[rustc_const_unstable(feature = "const_iter", issue = "92476")] |
| 2316 | impl<T> const IntoIterator for Option<T> { |
| 2317 | type Item = T; |
| 2318 | type IntoIter = IntoIter<T>; |
| 2319 | |
| 2320 | /// Returns a consuming iterator over the possibly contained value. |
| 2321 | /// |
| 2322 | /// # Examples |
| 2323 | /// |
| 2324 | /// ``` |
| 2325 | /// let x = Some("string"); |
| 2326 | /// let v: Vec<&str> = x.into_iter().collect(); |
| 2327 | /// assert_eq!(v, ["string"]); |
| 2328 | /// |
| 2329 | /// let x = None; |
| 2330 | /// let v: Vec<&str> = x.into_iter().collect(); |
| 2331 | /// assert!(v.is_empty()); |
| 2332 | /// ``` |
| 2333 | #[inline] |
| 2334 | fn into_iter(self) -> IntoIter<T> { |
| 2335 | IntoIter { inner: Item { opt: self } } |
| 2336 | } |
| 2337 | } |
| 2338 | |
| 2339 | #[stable(since = "1.4.0", feature = "option_iter")] |
| 2340 | impl<'a, T> IntoIterator for &'a Option<T> { |
| 2341 | type Item = &'a T; |
| 2342 | type IntoIter = Iter<'a, T>; |
| 2343 | |
| 2344 | fn into_iter(self) -> Iter<'a, T> { |
| 2345 | self.iter() |
| 2346 | } |
| 2347 | } |
| 2348 | |
| 2349 | #[stable(since = "1.4.0", feature = "option_iter")] |
| 2350 | impl<'a, T> IntoIterator for &'a mut Option<T> { |
| 2351 | type Item = &'a mut T; |
| 2352 | type IntoIter = IterMut<'a, T>; |
| 2353 | |
| 2354 | fn into_iter(self) -> IterMut<'a, T> { |
| 2355 | self.iter_mut() |
| 2356 | } |
| 2357 | } |
| 2358 | |
| 2359 | #[stable(since = "1.12.0", feature = "option_from")] |
| 2360 | #[rustc_const_unstable(feature = "const_convert", issue = "143773")] |
| 2361 | impl<T> const From<T> for Option<T> { |
| 2362 | /// Moves `val` into a new [`Some`]. |
| 2363 | /// |
| 2364 | /// # Examples |
| 2365 | /// |
| 2366 | /// ``` |
| 2367 | /// let o: Option<u8> = Option::from(67); |
| 2368 | /// |
| 2369 | /// assert_eq!(Some(67), o); |
| 2370 | /// ``` |
| 2371 | fn from(val: T) -> Option<T> { |
| 2372 | Some(val) |
| 2373 | } |
| 2374 | } |
| 2375 | |
| 2376 | #[stable(feature = "option_ref_from_ref_option", since = "1.30.0")] |
| 2377 | #[rustc_const_unstable(feature = "const_convert", issue = "143773")] |
| 2378 | impl<'a, T> const From<&'a Option<T>> for Option<&'a T> { |
| 2379 | /// Converts from `&Option<T>` to `Option<&T>`. |
| 2380 | /// |
| 2381 | /// # Examples |
| 2382 | /// |
| 2383 | /// Converts an <code>[Option]<[String]></code> into an <code>[Option]<[usize]></code>, preserving |
| 2384 | /// the original. The [`map`] method takes the `self` argument by value, consuming the original, |
| 2385 | /// so this technique uses `from` to first take an [`Option`] to a reference |
| 2386 | /// to the value inside the original. |
| 2387 | /// |
| 2388 | /// [`map`]: Option::map |
| 2389 | /// [String]: ../../std/string/struct.String.html "String" |
| 2390 | /// |
| 2391 | /// ``` |
| 2392 | /// let s: Option<String> = Some(String::from("Hello, Rustaceans!")); |
| 2393 | /// let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len()); |
| 2394 | /// |
| 2395 | /// println!("Can still print s: {s:?}"); |
| 2396 | /// |
| 2397 | /// assert_eq!(o, Some(18)); |
| 2398 | /// ``` |
| 2399 | fn from(o: &'a Option<T>) -> Option<&'a T> { |
| 2400 | o.as_ref() |
| 2401 | } |
| 2402 | } |
| 2403 | |
| 2404 | #[stable(feature = "option_ref_from_ref_option", since = "1.30.0")] |
| 2405 | #[rustc_const_unstable(feature = "const_convert", issue = "143773")] |
| 2406 | impl<'a, T> const From<&'a mut Option<T>> for Option<&'a mut T> { |
| 2407 | /// Converts from `&mut Option<T>` to `Option<&mut T>` |
| 2408 | /// |
| 2409 | /// # Examples |
| 2410 | /// |
| 2411 | /// ``` |
| 2412 | /// let mut s = Some(String::from("Hello")); |
| 2413 | /// let o: Option<&mut String> = Option::from(&mut s); |
| 2414 | /// |
| 2415 | /// match o { |
| 2416 | /// Some(t) => *t = String::from("Hello, Rustaceans!"), |
| 2417 | /// None => (), |
| 2418 | /// } |
| 2419 | /// |
| 2420 | /// assert_eq!(s, Some(String::from("Hello, Rustaceans!"))); |
| 2421 | /// ``` |
| 2422 | fn from(o: &'a mut Option<T>) -> Option<&'a mut T> { |
| 2423 | o.as_mut() |
| 2424 | } |
| 2425 | } |
| 2426 | |
| 2427 | // Ideally, LLVM should be able to optimize our derive code to this. |
| 2428 | // Once https://github.com/llvm/llvm-project/issues/52622 is fixed, we can |
| 2429 | // go back to deriving `PartialEq`. |
| 2430 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2431 | impl<T> crate::marker::StructuralPartialEq for Option<T> {} |
| 2432 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2433 | #[rustc_const_unstable(feature = "const_cmp", issue = "143800")] |
| 2434 | impl<T: [const] PartialEq> const PartialEq for Option<T> { |
| 2435 | #[inline] |
| 2436 | fn eq(&self, other: &Self) -> bool { |
| 2437 | // Spelling out the cases explicitly optimizes better than |
| 2438 | // `_ => false` |
| 2439 | match (self, other) { |
| 2440 | (Some(l), Some(r)) => *l == *r, |
| 2441 | (Some(_), None) => false, |
| 2442 | (None, Some(_)) => false, |
| 2443 | (None, None) => true, |
| 2444 | } |
| 2445 | } |
| 2446 | } |
| 2447 | |
| 2448 | // Manually implementing here somewhat improves codegen for |
| 2449 | // https://github.com/rust-lang/rust/issues/49892, although still |
| 2450 | // not optimal. |
| 2451 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2452 | #[rustc_const_unstable(feature = "const_cmp", issue = "143800")] |
| 2453 | impl<T: [const] PartialOrd> const PartialOrd for Option<T> { |
| 2454 | #[inline] |
| 2455 | fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> { |
| 2456 | match (self, other) { |
| 2457 | (Some(l), Some(r)) => l.partial_cmp(r), |
| 2458 | (Some(_), None) => Some(cmp::Ordering::Greater), |
| 2459 | (None, Some(_)) => Some(cmp::Ordering::Less), |
| 2460 | (None, None) => Some(cmp::Ordering::Equal), |
| 2461 | } |
| 2462 | } |
| 2463 | } |
| 2464 | |
| 2465 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2466 | #[rustc_const_unstable(feature = "const_cmp", issue = "143800")] |
| 2467 | impl<T: [const] Ord> const Ord for Option<T> { |
| 2468 | #[inline] |
| 2469 | fn cmp(&self, other: &Self) -> cmp::Ordering { |
| 2470 | match (self, other) { |
| 2471 | (Some(l), Some(r)) => l.cmp(r), |
| 2472 | (Some(_), None) => cmp::Ordering::Greater, |
| 2473 | (None, Some(_)) => cmp::Ordering::Less, |
| 2474 | (None, None) => cmp::Ordering::Equal, |
| 2475 | } |
| 2476 | } |
| 2477 | } |
| 2478 | |
| 2479 | ///////////////////////////////////////////////////////////////////////////// |
| 2480 | // The Option Iterators |
| 2481 | ///////////////////////////////////////////////////////////////////////////// |
| 2482 | |
| 2483 | #[derive(Clone, Debug)] |
| 2484 | struct Item<A> { |
| 2485 | opt: Option<A>, |
| 2486 | } |
| 2487 | |
| 2488 | #[rustc_const_unstable(feature = "const_iter", issue = "92476")] |
| 2489 | impl<A> const Iterator for Item<A> { |
| 2490 | type Item = A; |
| 2491 | |
| 2492 | #[inline] |
| 2493 | fn next(&mut self) -> Option<A> { |
| 2494 | self.opt.take() |
| 2495 | } |
| 2496 | |
| 2497 | #[inline] |
| 2498 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 2499 | let len = self.opt.len(); |
| 2500 | (len, Some(len)) |
| 2501 | } |
| 2502 | } |
| 2503 | |
| 2504 | impl<A> DoubleEndedIterator for Item<A> { |
| 2505 | #[inline] |
| 2506 | fn next_back(&mut self) -> Option<A> { |
| 2507 | self.opt.take() |
| 2508 | } |
| 2509 | } |
| 2510 | |
| 2511 | impl<A> ExactSizeIterator for Item<A> { |
| 2512 | #[inline] |
| 2513 | fn len(&self) -> usize { |
| 2514 | self.opt.len() |
| 2515 | } |
| 2516 | } |
| 2517 | impl<A> FusedIterator for Item<A> {} |
| 2518 | unsafe impl<A> TrustedLen for Item<A> {} |
| 2519 | |
| 2520 | /// An iterator over a reference to the [`Some`] variant of an [`Option`]. |
| 2521 | /// |
| 2522 | /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none. |
| 2523 | /// |
| 2524 | /// This `struct` is created by the [`Option::iter`] function. |
| 2525 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2526 | #[derive(Debug)] |
| 2527 | pub struct Iter<'a, A: 'a> { |
| 2528 | inner: Item<&'a A>, |
| 2529 | } |
| 2530 | |
| 2531 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2532 | impl<'a, A> Iterator for Iter<'a, A> { |
| 2533 | type Item = &'a A; |
| 2534 | |
| 2535 | #[inline] |
| 2536 | fn next(&mut self) -> Option<&'a A> { |
| 2537 | self.inner.next() |
| 2538 | } |
| 2539 | #[inline] |
| 2540 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 2541 | self.inner.size_hint() |
| 2542 | } |
| 2543 | } |
| 2544 | |
| 2545 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2546 | impl<'a, A> DoubleEndedIterator for Iter<'a, A> { |
| 2547 | #[inline] |
| 2548 | fn next_back(&mut self) -> Option<&'a A> { |
| 2549 | self.inner.next_back() |
| 2550 | } |
| 2551 | } |
| 2552 | |
| 2553 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2554 | impl<A> ExactSizeIterator for Iter<'_, A> {} |
| 2555 | |
| 2556 | #[stable(feature = "fused", since = "1.26.0")] |
| 2557 | impl<A> FusedIterator for Iter<'_, A> {} |
| 2558 | |
| 2559 | #[unstable(feature = "trusted_len", issue = "37572")] |
| 2560 | unsafe impl<A> TrustedLen for Iter<'_, A> {} |
| 2561 | |
| 2562 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2563 | impl<A> Clone for Iter<'_, A> { |
| 2564 | #[inline] |
| 2565 | fn clone(&self) -> Self { |
| 2566 | Iter { inner: self.inner.clone() } |
| 2567 | } |
| 2568 | } |
| 2569 | |
| 2570 | /// An iterator over a mutable reference to the [`Some`] variant of an [`Option`]. |
| 2571 | /// |
| 2572 | /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none. |
| 2573 | /// |
| 2574 | /// This `struct` is created by the [`Option::iter_mut`] function. |
| 2575 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2576 | #[derive(Debug)] |
| 2577 | pub struct IterMut<'a, A: 'a> { |
| 2578 | inner: Item<&'a mut A>, |
| 2579 | } |
| 2580 | |
| 2581 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2582 | impl<'a, A> Iterator for IterMut<'a, A> { |
| 2583 | type Item = &'a mut A; |
| 2584 | |
| 2585 | #[inline] |
| 2586 | fn next(&mut self) -> Option<&'a mut A> { |
| 2587 | self.inner.next() |
| 2588 | } |
| 2589 | #[inline] |
| 2590 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 2591 | self.inner.size_hint() |
| 2592 | } |
| 2593 | } |
| 2594 | |
| 2595 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2596 | impl<'a, A> DoubleEndedIterator for IterMut<'a, A> { |
| 2597 | #[inline] |
| 2598 | fn next_back(&mut self) -> Option<&'a mut A> { |
| 2599 | self.inner.next_back() |
| 2600 | } |
| 2601 | } |
| 2602 | |
| 2603 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2604 | impl<A> ExactSizeIterator for IterMut<'_, A> {} |
| 2605 | |
| 2606 | #[stable(feature = "fused", since = "1.26.0")] |
| 2607 | impl<A> FusedIterator for IterMut<'_, A> {} |
| 2608 | #[unstable(feature = "trusted_len", issue = "37572")] |
| 2609 | unsafe impl<A> TrustedLen for IterMut<'_, A> {} |
| 2610 | |
| 2611 | /// An iterator over the value in [`Some`] variant of an [`Option`]. |
| 2612 | /// |
| 2613 | /// The iterator yields one value if the [`Option`] is a [`Some`], otherwise none. |
| 2614 | /// |
| 2615 | /// This `struct` is created by the [`Option::into_iter`] function. |
| 2616 | #[derive(Clone, Debug)] |
| 2617 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2618 | pub struct IntoIter<A> { |
| 2619 | inner: Item<A>, |
| 2620 | } |
| 2621 | |
| 2622 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2623 | #[rustc_const_unstable(feature = "const_iter", issue = "92476")] |
| 2624 | impl<A> const Iterator for IntoIter<A> { |
| 2625 | type Item = A; |
| 2626 | |
| 2627 | #[inline] |
| 2628 | fn next(&mut self) -> Option<A> { |
| 2629 | self.inner.next() |
| 2630 | } |
| 2631 | #[inline] |
| 2632 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 2633 | self.inner.size_hint() |
| 2634 | } |
| 2635 | } |
| 2636 | |
| 2637 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2638 | impl<A> DoubleEndedIterator for IntoIter<A> { |
| 2639 | #[inline] |
| 2640 | fn next_back(&mut self) -> Option<A> { |
| 2641 | self.inner.next_back() |
| 2642 | } |
| 2643 | } |
| 2644 | |
| 2645 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2646 | impl<A> ExactSizeIterator for IntoIter<A> {} |
| 2647 | |
| 2648 | #[stable(feature = "fused", since = "1.26.0")] |
| 2649 | impl<A> FusedIterator for IntoIter<A> {} |
| 2650 | |
| 2651 | #[unstable(feature = "trusted_len", issue = "37572")] |
| 2652 | unsafe impl<A> TrustedLen for IntoIter<A> {} |
| 2653 | |
| 2654 | /// The iterator produced by [`Option::into_flat_iter`]. See its documentation for more. |
| 2655 | #[derive(Clone, Debug)] |
| 2656 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2657 | pub struct OptionFlatten<A> { |
| 2658 | iter: Option<A>, |
| 2659 | } |
| 2660 | |
| 2661 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2662 | impl<A: Iterator> Iterator for OptionFlatten<A> { |
| 2663 | type Item = A::Item; |
| 2664 | |
| 2665 | fn next(&mut self) -> Option<Self::Item> { |
| 2666 | self.iter.as_mut()?.next() |
| 2667 | } |
| 2668 | |
| 2669 | fn size_hint(&self) -> (usize, Option<usize>) { |
| 2670 | self.iter.as_ref().map(|i| i.size_hint()).unwrap_or((0, Some(0))) |
| 2671 | } |
| 2672 | } |
| 2673 | |
| 2674 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2675 | impl<A: DoubleEndedIterator> DoubleEndedIterator for OptionFlatten<A> { |
| 2676 | fn next_back(&mut self) -> Option<Self::Item> { |
| 2677 | self.iter.as_mut()?.next_back() |
| 2678 | } |
| 2679 | } |
| 2680 | |
| 2681 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2682 | impl<A: ExactSizeIterator> ExactSizeIterator for OptionFlatten<A> {} |
| 2683 | |
| 2684 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2685 | impl<A: FusedIterator> FusedIterator for OptionFlatten<A> {} |
| 2686 | |
| 2687 | #[unstable(feature = "option_into_flat_iter", issue = "148441")] |
| 2688 | unsafe impl<A: TrustedLen> TrustedLen for OptionFlatten<A> {} |
| 2689 | |
| 2690 | ///////////////////////////////////////////////////////////////////////////// |
| 2691 | // FromIterator |
| 2692 | ///////////////////////////////////////////////////////////////////////////// |
| 2693 | |
| 2694 | #[stable(feature = "rust1", since = "1.0.0")] |
| 2695 | impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> { |
| 2696 | /// Takes each element in the [`Iterator`]: if it is [`None`][Option::None], |
| 2697 | /// no further elements are taken, and the [`None`][Option::None] is |
| 2698 | /// returned. Should no [`None`][Option::None] occur, a container of type |
| 2699 | /// `V` containing the values of each [`Option`] is returned. |
| 2700 | /// |
| 2701 | /// # Examples |
| 2702 | /// |
| 2703 | /// Here is an example which increments every integer in a vector. |
| 2704 | /// We use the checked variant of `add` that returns `None` when the |
| 2705 | /// calculation would result in an overflow. |
| 2706 | /// |
| 2707 | /// ``` |
| 2708 | /// let items = vec![0_u16, 1, 2]; |
| 2709 | /// |
| 2710 | /// let res: Option<Vec<u16>> = items |
| 2711 | /// .iter() |
| 2712 | /// .map(|x| x.checked_add(1)) |
| 2713 | /// .collect(); |
| 2714 | /// |
| 2715 | /// assert_eq!(res, Some(vec![1, 2, 3])); |
| 2716 | /// ``` |
| 2717 | /// |
| 2718 | /// As you can see, this will return the expected, valid items. |
| 2719 | /// |
| 2720 | /// Here is another example that tries to subtract one from another list |
| 2721 | /// of integers, this time checking for underflow: |
| 2722 | /// |
| 2723 | /// ``` |
| 2724 | /// let items = vec![2_u16, 1, 0]; |
| 2725 | /// |
| 2726 | /// let res: Option<Vec<u16>> = items |
| 2727 | /// .iter() |
| 2728 | /// .map(|x| x.checked_sub(1)) |
| 2729 | /// .collect(); |
| 2730 | /// |
| 2731 | /// assert_eq!(res, None); |
| 2732 | /// ``` |
| 2733 | /// |
| 2734 | /// Since the last element is zero, it would underflow. Thus, the resulting |
| 2735 | /// value is `None`. |
| 2736 | /// |
| 2737 | /// Here is a variation on the previous example, showing that no |
| 2738 | /// further elements are taken from `iter` after the first `None`. |
| 2739 | /// |
| 2740 | /// ``` |
| 2741 | /// let items = vec![3_u16, 2, 1, 10]; |
| 2742 | /// |
| 2743 | /// let mut shared = 0; |
| 2744 | /// |
| 2745 | /// let res: Option<Vec<u16>> = items |
| 2746 | /// .iter() |
| 2747 | /// .map(|x| { shared += x; x.checked_sub(2) }) |
| 2748 | /// .collect(); |
| 2749 | /// |
| 2750 | /// assert_eq!(res, None); |
| 2751 | /// assert_eq!(shared, 6); |
| 2752 | /// ``` |
| 2753 | /// |
| 2754 | /// Since the third element caused an underflow, no further elements were taken, |
| 2755 | /// so the final value of `shared` is 6 (= `3 + 2 + 1`), not 16. |
| 2756 | #[inline] |
| 2757 | fn from_iter<I: IntoIterator<Item = Option<A>>>(iter: I) -> Option<V> { |
| 2758 | iter::try_process(iter.into_iter(), |i| i.collect()) |
| 2759 | } |
| 2760 | } |
| 2761 | |
| 2762 | #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")] |
| 2763 | #[rustc_const_unstable(feature = "const_try", issue = "74935")] |
| 2764 | impl<T> const ops::Try for Option<T> { |
| 2765 | type Output = T; |
| 2766 | type Residual = Option<convert::Infallible>; |
| 2767 | |
| 2768 | #[inline] |
| 2769 | fn from_output(output: Self::Output) -> Self { |
| 2770 | Some(output) |
| 2771 | } |
| 2772 | |
| 2773 | #[inline] |
| 2774 | fn branch(self) -> ControlFlow<Self::Residual, Self::Output> { |
| 2775 | match self { |
| 2776 | Some(v) => ControlFlow::Continue(v), |
| 2777 | None => ControlFlow::Break(None), |
| 2778 | } |
| 2779 | } |
| 2780 | } |
| 2781 | |
| 2782 | #[unstable(feature = "try_trait_v2", issue = "84277", old_name = "try_trait")] |
| 2783 | #[rustc_const_unstable(feature = "const_try", issue = "74935")] |
| 2784 | // Note: manually specifying the residual type instead of using the default to work around |
| 2785 | // https://github.com/rust-lang/rust/issues/99940 |
| 2786 | impl<T> const ops::FromResidual<Option<convert::Infallible>> for Option<T> { |
| 2787 | #[inline] |
| 2788 | fn from_residual(residual: Option<convert::Infallible>) -> Self { |
| 2789 | match residual { |
| 2790 | None => None, |
| 2791 | } |
| 2792 | } |
| 2793 | } |
| 2794 | |
| 2795 | #[diagnostic::do_not_recommend] |
| 2796 | #[unstable(feature = "try_trait_v2_yeet", issue = "96374")] |
| 2797 | #[rustc_const_unstable(feature = "const_try", issue = "74935")] |
| 2798 | impl<T> const ops::FromResidual<ops::Yeet<()>> for Option<T> { |
| 2799 | #[inline] |
| 2800 | fn from_residual(ops::Yeet(()): ops::Yeet<()>) -> Self { |
| 2801 | None |
| 2802 | } |
| 2803 | } |
| 2804 | |
| 2805 | #[unstable(feature = "try_trait_v2_residual", issue = "91285")] |
| 2806 | #[rustc_const_unstable(feature = "const_try", issue = "74935")] |
| 2807 | impl<T> const ops::Residual<T> for Option<convert::Infallible> { |
| 2808 | type TryType = Option<T>; |
| 2809 | } |
| 2810 | |
| 2811 | impl<T> Option<Option<T>> { |
| 2812 | /// Converts from `Option<Option<T>>` to `Option<T>`. |
| 2813 | /// |
| 2814 | /// # Examples |
| 2815 | /// |
| 2816 | /// Basic usage: |
| 2817 | /// |
| 2818 | /// ``` |
| 2819 | /// let x: Option<Option<u32>> = Some(Some(6)); |
| 2820 | /// assert_eq!(Some(6), x.flatten()); |
| 2821 | /// |
| 2822 | /// let x: Option<Option<u32>> = Some(None); |
| 2823 | /// assert_eq!(None, x.flatten()); |
| 2824 | /// |
| 2825 | /// let x: Option<Option<u32>> = None; |
| 2826 | /// assert_eq!(None, x.flatten()); |
| 2827 | /// ``` |
| 2828 | /// |
| 2829 | /// Flattening only removes one level of nesting at a time: |
| 2830 | /// |
| 2831 | /// ``` |
| 2832 | /// let x: Option<Option<Option<u32>>> = Some(Some(Some(6))); |
| 2833 | /// assert_eq!(Some(Some(6)), x.flatten()); |
| 2834 | /// assert_eq!(Some(6), x.flatten().flatten()); |
| 2835 | /// ``` |
| 2836 | #[inline] |
| 2837 | #[stable(feature = "option_flattening", since = "1.40.0")] |
| 2838 | #[rustc_allow_const_fn_unstable(const_precise_live_drops)] |
| 2839 | #[rustc_const_stable(feature = "const_option", since = "1.83.0")] |
| 2840 | pub const fn flatten(self) -> Option<T> { |
| 2841 | // FIXME(const-hack): could be written with `and_then` |
| 2842 | match self { |
| 2843 | Some(inner) => inner, |
| 2844 | None => None, |
| 2845 | } |
| 2846 | } |
| 2847 | } |
| 2848 | |
| 2849 | impl<'a, T> Option<&'a Option<T>> { |
| 2850 | /// Converts from `Option<&Option<T>>` to `Option<&T>`. |
| 2851 | /// |
| 2852 | /// # Examples |
| 2853 | /// |
| 2854 | /// Basic usage: |
| 2855 | /// |
| 2856 | /// ``` |
| 2857 | /// #![feature(option_reference_flattening)] |
| 2858 | /// |
| 2859 | /// let x: Option<&Option<u32>> = Some(&Some(6)); |
| 2860 | /// assert_eq!(Some(&6), x.flatten_ref()); |
| 2861 | /// |
| 2862 | /// let x: Option<&Option<u32>> = Some(&None); |
| 2863 | /// assert_eq!(None, x.flatten_ref()); |
| 2864 | /// |
| 2865 | /// let x: Option<&Option<u32>> = None; |
| 2866 | /// assert_eq!(None, x.flatten_ref()); |
| 2867 | /// ``` |
| 2868 | #[inline] |
| 2869 | #[unstable(feature = "option_reference_flattening", issue = "149221")] |
| 2870 | pub const fn flatten_ref(self) -> Option<&'a T> { |
| 2871 | match self { |
| 2872 | Some(inner) => inner.as_ref(), |
| 2873 | None => None, |
| 2874 | } |
| 2875 | } |
| 2876 | } |
| 2877 | |
| 2878 | impl<'a, T> Option<&'a mut Option<T>> { |
| 2879 | /// Converts from `Option<&mut Option<T>>` to `&Option<T>`. |
| 2880 | /// |
| 2881 | /// # Examples |
| 2882 | /// |
| 2883 | /// Basic usage: |
| 2884 | /// |
| 2885 | /// ``` |
| 2886 | /// #![feature(option_reference_flattening)] |
| 2887 | /// |
| 2888 | /// let y = &mut Some(6); |
| 2889 | /// let x: Option<&mut Option<u32>> = Some(y); |
| 2890 | /// assert_eq!(Some(&6), x.flatten_ref()); |
| 2891 | /// |
| 2892 | /// let y: &mut Option<u32> = &mut None; |
| 2893 | /// let x: Option<&mut Option<u32>> = Some(y); |
| 2894 | /// assert_eq!(None, x.flatten_ref()); |
| 2895 | /// |
| 2896 | /// let x: Option<&mut Option<u32>> = None; |
| 2897 | /// assert_eq!(None, x.flatten_ref()); |
| 2898 | /// ``` |
| 2899 | #[inline] |
| 2900 | #[unstable(feature = "option_reference_flattening", issue = "149221")] |
| 2901 | pub const fn flatten_ref(self) -> Option<&'a T> { |
| 2902 | match self { |
| 2903 | Some(inner) => inner.as_ref(), |
| 2904 | None => None, |
| 2905 | } |
| 2906 | } |
| 2907 | |
| 2908 | /// Converts from `Option<&mut Option<T>>` to `Option<&mut T>`. |
| 2909 | /// |
| 2910 | /// # Examples |
| 2911 | /// |
| 2912 | /// Basic usage: |
| 2913 | /// |
| 2914 | /// ``` |
| 2915 | /// #![feature(option_reference_flattening)] |
| 2916 | /// |
| 2917 | /// let y: &mut Option<u32> = &mut Some(6); |
| 2918 | /// let x: Option<&mut Option<u32>> = Some(y); |
| 2919 | /// assert_eq!(Some(&mut 6), x.flatten_mut()); |
| 2920 | /// |
| 2921 | /// let y: &mut Option<u32> = &mut None; |
| 2922 | /// let x: Option<&mut Option<u32>> = Some(y); |
| 2923 | /// assert_eq!(None, x.flatten_mut()); |
| 2924 | /// |
| 2925 | /// let x: Option<&mut Option<u32>> = None; |
| 2926 | /// assert_eq!(None, x.flatten_mut()); |
| 2927 | /// ``` |
| 2928 | #[inline] |
| 2929 | #[unstable(feature = "option_reference_flattening", issue = "149221")] |
| 2930 | pub const fn flatten_mut(self) -> Option<&'a mut T> { |
| 2931 | match self { |
| 2932 | Some(inner) => inner.as_mut(), |
| 2933 | None => None, |
| 2934 | } |
| 2935 | } |
| 2936 | } |
| 2937 | |
| 2938 | impl<T, const N: usize> [Option<T>; N] { |
| 2939 | /// Transposes a `[Option<T>; N]` into a `Option<[T; N]>`. |
| 2940 | /// |
| 2941 | /// # Examples |
| 2942 | /// |
| 2943 | /// ``` |
| 2944 | /// #![feature(option_array_transpose)] |
| 2945 | /// # use std::option::Option; |
| 2946 | /// |
| 2947 | /// let data = [Some(0); 1000]; |
| 2948 | /// let data: Option<[u8; 1000]> = data.transpose(); |
| 2949 | /// assert_eq!(data, Some([0; 1000])); |
| 2950 | /// |
| 2951 | /// let data = [Some(0), None]; |
| 2952 | /// let data: Option<[u8; 2]> = data.transpose(); |
| 2953 | /// assert_eq!(data, None); |
| 2954 | /// ``` |
| 2955 | #[inline] |
| 2956 | #[unstable(feature = "option_array_transpose", issue = "130828")] |
| 2957 | pub fn transpose(self) -> Option<[T; N]> { |
| 2958 | self.try_map(core::convert::identity) |
| 2959 | } |
| 2960 | } |