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1 | // Copyright 2014 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | //! Traits for conversions between types. | |
12 | //! | |
62682a34 SL |
13 | //! The traits in this module provide a general way to talk about conversions |
14 | //! from one type to another. They follow the standard Rust conventions of | |
15 | //! `as`/`into`/`from`. | |
9346a6ac | 16 | //! |
62682a34 SL |
17 | //! Like many traits, these are often used as bounds for generic functions, to |
18 | //! support arguments of multiple types. | |
9346a6ac | 19 | //! |
cc61c64b XL |
20 | //! - Implement the `As*` traits for reference-to-reference conversions |
21 | //! - Implement the [`Into`] trait when you want to consume the value in the conversion | |
32a655c1 SL |
22 | //! - The [`From`] trait is the most flexible, useful for value _and_ reference conversions |
23 | //! - The [`TryFrom`] and [`TryInto`] traits behave like [`From`] and [`Into`], but allow for the | |
a7813a04 | 24 | //! conversion to fail |
7453a54e | 25 | //! |
32a655c1 SL |
26 | //! As a library author, you should prefer implementing [`From<T>`][`From`] or |
27 | //! [`TryFrom<T>`][`TryFrom`] rather than [`Into<U>`][`Into`] or [`TryInto<U>`][`TryInto`], | |
28 | //! as [`From`] and [`TryFrom`] provide greater flexibility and offer | |
cc61c64b XL |
29 | //! equivalent [`Into`] or [`TryInto`] implementations for free, thanks to a |
30 | //! blanket implementation in the standard library. | |
7453a54e | 31 | //! |
cc61c64b | 32 | //! # Generic Implementations |
7453a54e | 33 | //! |
32a655c1 SL |
34 | //! - [`AsRef`] and [`AsMut`] auto-dereference if the inner type is a reference |
35 | //! - [`From`]`<U> for T` implies [`Into`]`<T> for U` | |
36 | //! - [`TryFrom`]`<U> for T` implies [`TryInto`]`<T> for U` | |
cc61c64b XL |
37 | //! - [`From`] and [`Into`] are reflexive, which means that all types can |
38 | //! `into` themselves and `from` themselves | |
7453a54e | 39 | //! |
9346a6ac | 40 | //! See each trait for usage examples. |
32a655c1 SL |
41 | //! |
42 | //! [`Into`]: trait.Into.html | |
43 | //! [`From`]: trait.From.html | |
44 | //! [`TryFrom`]: trait.TryFrom.html | |
45 | //! [`TryInto`]: trait.TryInto.html | |
46 | //! [`AsRef`]: trait.AsRef.html | |
47 | //! [`AsMut`]: trait.AsMut.html | |
c34b1796 AL |
48 | |
49 | #![stable(feature = "rust1", since = "1.0.0")] | |
50 | ||
b7449926 XL |
51 | /// An identity function. |
52 | /// | |
53 | /// Two things are important to note about this function: | |
54 | /// | |
55 | /// - It is not always equivalent to a closure like `|x| x` since the | |
56 | /// closure may coerce `x` into a different type. | |
57 | /// | |
58 | /// - It moves the input `x` passed to the function. | |
59 | /// | |
60 | /// While it might seem strange to have a function that just returns back the | |
61 | /// input, there are some interesting uses. | |
62 | /// | |
63 | /// # Examples | |
64 | /// | |
65 | /// Using `identity` to do nothing among other interesting functions: | |
66 | /// | |
67 | /// ```rust | |
68 | /// #![feature(convert_id)] | |
69 | /// use std::convert::identity; | |
70 | /// | |
71 | /// fn manipulation(x: u32) -> u32 { | |
72 | /// // Let's assume that this function does something interesting. | |
73 | /// x + 1 | |
74 | /// } | |
75 | /// | |
76 | /// let _arr = &[identity, manipulation]; | |
77 | /// ``` | |
78 | /// | |
79 | /// Using `identity` to get a function that changes nothing in a conditional: | |
80 | /// | |
81 | /// ```rust | |
82 | /// #![feature(convert_id)] | |
83 | /// use std::convert::identity; | |
84 | /// | |
85 | /// # let condition = true; | |
86 | /// | |
87 | /// # fn manipulation(x: u32) -> u32 { x + 1 } | |
88 | /// | |
89 | /// let do_stuff = if condition { manipulation } else { identity }; | |
90 | /// | |
91 | /// // do more interesting stuff.. | |
92 | /// | |
93 | /// let _results = do_stuff(42); | |
94 | /// ``` | |
95 | /// | |
96 | /// Using `identity` to keep the `Some` variants of an iterator of `Option<T>`: | |
97 | /// | |
98 | /// ```rust | |
99 | /// #![feature(convert_id)] | |
100 | /// use std::convert::identity; | |
101 | /// | |
102 | /// let iter = vec![Some(1), None, Some(3)].into_iter(); | |
103 | /// let filtered = iter.filter_map(identity).collect::<Vec<_>>(); | |
104 | /// assert_eq!(vec![1, 3], filtered); | |
105 | /// ``` | |
106 | #[unstable(feature = "convert_id", issue = "53500")] | |
107 | #[rustc_const_unstable(feature = "const_convert_id")] | |
108 | #[inline] | |
109 | pub const fn identity<T>(x: T) -> T { x } | |
110 | ||
cc61c64b XL |
111 | /// A cheap reference-to-reference conversion. Used to convert a value to a |
112 | /// reference value within generic code. | |
113 | /// | |
114 | /// `AsRef` is very similar to, but serves a slightly different purpose than, | |
115 | /// [`Borrow`]. | |
116 | /// | |
117 | /// `AsRef` is to be used when wishing to convert to a reference of another | |
118 | /// type. | |
119 | /// `Borrow` is more related to the notion of taking the reference. It is | |
120 | /// useful when wishing to abstract over the type of reference | |
121 | /// (`&T`, `&mut T`) or allow both the referenced and owned type to be treated | |
122 | /// in the same manner. | |
9346a6ac | 123 | /// |
cc61c64b XL |
124 | /// The key difference between the two traits is the intention: |
125 | /// | |
8faf50e0 XL |
126 | /// - Use `AsRef` when the goal is to simply convert into a reference |
127 | /// - Use `Borrow` when the goal is related to writing code that is agnostic to | |
128 | /// the type of borrow and whether it is a reference or value | |
cc61c64b XL |
129 | /// |
130 | /// See [the book][book] for a more detailed comparison. | |
d9579d0f | 131 | /// |
041b39d2 | 132 | /// [book]: ../../book/first-edition/borrow-and-asref.html |
9e0c209e | 133 | /// [`Borrow`]: ../../std/borrow/trait.Borrow.html |
d9579d0f | 134 | /// |
cc61c64b XL |
135 | /// **Note: this trait must not fail**. If the conversion can fail, use a |
136 | /// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`]. | |
9e0c209e SL |
137 | /// |
138 | /// [`Option<T>`]: ../../std/option/enum.Option.html | |
139 | /// [`Result<T, E>`]: ../../std/result/enum.Result.html | |
7453a54e | 140 | /// |
cc61c64b XL |
141 | /// # Generic Implementations |
142 | /// | |
143 | /// - `AsRef` auto-dereferences if the inner type is a reference or a mutable | |
144 | /// reference (e.g.: `foo.as_ref()` will work the same if `foo` has type | |
145 | /// `&mut Foo` or `&&mut Foo`) | |
146 | /// | |
9346a6ac AL |
147 | /// # Examples |
148 | /// | |
9e0c209e SL |
149 | /// Both [`String`] and `&str` implement `AsRef<str>`: |
150 | /// | |
151 | /// [`String`]: ../../std/string/struct.String.html | |
9346a6ac AL |
152 | /// |
153 | /// ``` | |
154 | /// fn is_hello<T: AsRef<str>>(s: T) { | |
155 | /// assert_eq!("hello", s.as_ref()); | |
156 | /// } | |
157 | /// | |
158 | /// let s = "hello"; | |
159 | /// is_hello(s); | |
160 | /// | |
161 | /// let s = "hello".to_string(); | |
162 | /// is_hello(s); | |
163 | /// ``` | |
7453a54e | 164 | /// |
c34b1796 AL |
165 | #[stable(feature = "rust1", since = "1.0.0")] |
166 | pub trait AsRef<T: ?Sized> { | |
9346a6ac | 167 | /// Performs the conversion. |
c34b1796 AL |
168 | #[stable(feature = "rust1", since = "1.0.0")] |
169 | fn as_ref(&self) -> &T; | |
170 | } | |
171 | ||
172 | /// A cheap, mutable reference-to-mutable reference conversion. | |
7453a54e | 173 | /// |
cc61c64b XL |
174 | /// This trait is similar to `AsRef` but used for converting between mutable |
175 | /// references. | |
176 | /// | |
177 | /// **Note: this trait must not fail**. If the conversion can fail, use a | |
178 | /// dedicated method which returns an [`Option<T>`] or a [`Result<T, E>`]. | |
9e0c209e SL |
179 | /// |
180 | /// [`Option<T>`]: ../../std/option/enum.Option.html | |
181 | /// [`Result<T, E>`]: ../../std/result/enum.Result.html | |
182 | /// | |
cc61c64b XL |
183 | /// # Generic Implementations |
184 | /// | |
2c00a5a8 XL |
185 | /// - `AsMut` auto-dereferences if the inner type is a mutable reference |
186 | /// (e.g.: `foo.as_mut()` will work the same if `foo` has type `&mut Foo` | |
187 | /// or `&mut &mut Foo`) | |
cc61c64b | 188 | /// |
9e0c209e SL |
189 | /// # Examples |
190 | /// | |
191 | /// [`Box<T>`] implements `AsMut<T>`: | |
192 | /// | |
193 | /// [`Box<T>`]: ../../std/boxed/struct.Box.html | |
194 | /// | |
195 | /// ``` | |
196 | /// fn add_one<T: AsMut<u64>>(num: &mut T) { | |
197 | /// *num.as_mut() += 1; | |
198 | /// } | |
199 | /// | |
200 | /// let mut boxed_num = Box::new(0); | |
201 | /// add_one(&mut boxed_num); | |
202 | /// assert_eq!(*boxed_num, 1); | |
203 | /// ``` | |
7453a54e | 204 | /// |
7453a54e | 205 | /// |
c34b1796 AL |
206 | #[stable(feature = "rust1", since = "1.0.0")] |
207 | pub trait AsMut<T: ?Sized> { | |
9346a6ac | 208 | /// Performs the conversion. |
c34b1796 AL |
209 | #[stable(feature = "rust1", since = "1.0.0")] |
210 | fn as_mut(&mut self) -> &mut T; | |
211 | } | |
212 | ||
cc61c64b XL |
213 | /// A conversion that consumes `self`, which may or may not be expensive. The |
214 | /// reciprocal of [`From`][From]. | |
215 | /// | |
216 | /// **Note: this trait must not fail**. If the conversion can fail, use | |
217 | /// [`TryInto`] or a dedicated method which returns an [`Option<T>`] or a | |
218 | /// [`Result<T, E>`]. | |
9346a6ac | 219 | /// |
cc61c64b XL |
220 | /// Library authors should not directly implement this trait, but should prefer |
221 | /// implementing the [`From`][From] trait, which offers greater flexibility and | |
222 | /// provides an equivalent `Into` implementation for free, thanks to a blanket | |
223 | /// implementation in the standard library. | |
7453a54e | 224 | /// |
cc61c64b XL |
225 | /// # Generic Implementations |
226 | /// | |
227 | /// - [`From<T>`][From]` for U` implies `Into<U> for T` | |
228 | /// - [`into`] is reflexive, which means that `Into<T> for T` is implemented | |
7453a54e | 229 | /// |
7cac9316 XL |
230 | /// # Implementing `Into` |
231 | /// | |
232 | /// There is one exception to implementing `Into`, and it's kind of esoteric. | |
233 | /// If the destination type is not part of the current crate, and it uses a | |
234 | /// generic variable, then you can't implement `From` directly. For example, | |
235 | /// take this crate: | |
236 | /// | |
237 | /// ```compile_fail | |
238 | /// struct Wrapper<T>(Vec<T>); | |
239 | /// impl<T> From<Wrapper<T>> for Vec<T> { | |
240 | /// fn from(w: Wrapper<T>) -> Vec<T> { | |
241 | /// w.0 | |
242 | /// } | |
243 | /// } | |
244 | /// ``` | |
245 | /// | |
246 | /// To fix this, you can implement `Into` directly: | |
247 | /// | |
248 | /// ``` | |
249 | /// struct Wrapper<T>(Vec<T>); | |
250 | /// impl<T> Into<Vec<T>> for Wrapper<T> { | |
251 | /// fn into(self) -> Vec<T> { | |
252 | /// self.0 | |
253 | /// } | |
254 | /// } | |
255 | /// ``` | |
256 | /// | |
257 | /// This won't always allow the conversion: for example, `try!` and `?` | |
258 | /// always use `From`. However, in most cases, people use `Into` to do the | |
259 | /// conversions, and this will allow that. | |
260 | /// | |
261 | /// In almost all cases, you should try to implement `From`, then fall back | |
262 | /// to `Into` if `From` can't be implemented. | |
263 | /// | |
9346a6ac AL |
264 | /// # Examples |
265 | /// | |
9e0c209e | 266 | /// [`String`] implements `Into<Vec<u8>>`: |
9346a6ac AL |
267 | /// |
268 | /// ``` | |
269 | /// fn is_hello<T: Into<Vec<u8>>>(s: T) { | |
270 | /// let bytes = b"hello".to_vec(); | |
271 | /// assert_eq!(bytes, s.into()); | |
272 | /// } | |
273 | /// | |
274 | /// let s = "hello".to_string(); | |
275 | /// is_hello(s); | |
276 | /// ``` | |
7453a54e | 277 | /// |
9e0c209e SL |
278 | /// [`TryInto`]: trait.TryInto.html |
279 | /// [`Option<T>`]: ../../std/option/enum.Option.html | |
280 | /// [`Result<T, E>`]: ../../std/result/enum.Result.html | |
281 | /// [`String`]: ../../std/string/struct.String.html | |
282 | /// [From]: trait.From.html | |
cc61c64b | 283 | /// [`into`]: trait.Into.html#tymethod.into |
c34b1796 AL |
284 | #[stable(feature = "rust1", since = "1.0.0")] |
285 | pub trait Into<T>: Sized { | |
9346a6ac | 286 | /// Performs the conversion. |
c34b1796 AL |
287 | #[stable(feature = "rust1", since = "1.0.0")] |
288 | fn into(self) -> T; | |
289 | } | |
290 | ||
cc61c64b XL |
291 | /// Simple and safe type conversions in to `Self`. It is the reciprocal of |
292 | /// `Into`. | |
293 | /// | |
294 | /// This trait is useful when performing error handling as described by | |
295 | /// [the book][book] and is closely related to the `?` operator. | |
9346a6ac | 296 | /// |
cc61c64b XL |
297 | /// When constructing a function that is capable of failing the return type |
298 | /// will generally be of the form `Result<T, E>`. | |
299 | /// | |
300 | /// The `From` trait allows for simplification of error handling by providing a | |
301 | /// means of returning a single error type that encapsulates numerous possible | |
302 | /// erroneous situations. | |
303 | /// | |
304 | /// This trait is not limited to error handling, rather the general case for | |
305 | /// this trait would be in any type conversions to have an explicit definition | |
306 | /// of how they are performed. | |
307 | /// | |
308 | /// **Note: this trait must not fail**. If the conversion can fail, use | |
309 | /// [`TryFrom`] or a dedicated method which returns an [`Option<T>`] or a | |
310 | /// [`Result<T, E>`]. | |
311 | /// | |
312 | /// # Generic Implementations | |
313 | /// | |
314 | /// - `From<T> for U` implies [`Into<U>`]` for T` | |
315 | /// - [`from`] is reflexive, which means that `From<T> for T` is implemented | |
7453a54e | 316 | /// |
9346a6ac AL |
317 | /// # Examples |
318 | /// | |
9e0c209e | 319 | /// [`String`] implements `From<&str>`: |
9346a6ac AL |
320 | /// |
321 | /// ``` | |
9346a6ac | 322 | /// let string = "hello".to_string(); |
bd371182 | 323 | /// let other_string = String::from("hello"); |
9346a6ac AL |
324 | /// |
325 | /// assert_eq!(string, other_string); | |
326 | /// ``` | |
7453a54e | 327 | /// |
cc61c64b XL |
328 | /// An example usage for error handling: |
329 | /// | |
330 | /// ``` | |
331 | /// use std::io::{self, Read}; | |
332 | /// use std::num; | |
333 | /// | |
334 | /// enum CliError { | |
335 | /// IoError(io::Error), | |
336 | /// ParseError(num::ParseIntError), | |
337 | /// } | |
338 | /// | |
339 | /// impl From<io::Error> for CliError { | |
340 | /// fn from(error: io::Error) -> Self { | |
341 | /// CliError::IoError(error) | |
342 | /// } | |
343 | /// } | |
344 | /// | |
345 | /// impl From<num::ParseIntError> for CliError { | |
346 | /// fn from(error: num::ParseIntError) -> Self { | |
347 | /// CliError::ParseError(error) | |
348 | /// } | |
349 | /// } | |
350 | /// | |
351 | /// fn open_and_parse_file(file_name: &str) -> Result<i32, CliError> { | |
352 | /// let mut file = std::fs::File::open("test")?; | |
353 | /// let mut contents = String::new(); | |
354 | /// file.read_to_string(&mut contents)?; | |
355 | /// let num: i32 = contents.trim().parse()?; | |
356 | /// Ok(num) | |
357 | /// } | |
358 | /// ``` | |
7453a54e | 359 | /// |
9e0c209e SL |
360 | /// [`TryFrom`]: trait.TryFrom.html |
361 | /// [`Option<T>`]: ../../std/option/enum.Option.html | |
362 | /// [`Result<T, E>`]: ../../std/result/enum.Result.html | |
363 | /// [`String`]: ../../std/string/struct.String.html | |
c30ab7b3 | 364 | /// [`Into<U>`]: trait.Into.html |
cc61c64b | 365 | /// [`from`]: trait.From.html#tymethod.from |
041b39d2 | 366 | /// [book]: ../../book/first-edition/error-handling.html |
c34b1796 | 367 | #[stable(feature = "rust1", since = "1.0.0")] |
b039eaaf | 368 | pub trait From<T>: Sized { |
9346a6ac | 369 | /// Performs the conversion. |
c34b1796 | 370 | #[stable(feature = "rust1", since = "1.0.0")] |
7cac9316 | 371 | fn from(_: T) -> Self; |
c34b1796 AL |
372 | } |
373 | ||
cc61c64b XL |
374 | /// An attempted conversion that consumes `self`, which may or may not be |
375 | /// expensive. | |
a7813a04 | 376 | /// |
cc61c64b XL |
377 | /// Library authors should not directly implement this trait, but should prefer |
378 | /// implementing the [`TryFrom`] trait, which offers greater flexibility and | |
379 | /// provides an equivalent `TryInto` implementation for free, thanks to a | |
7cac9316 XL |
380 | /// blanket implementation in the standard library. For more information on this, |
381 | /// see the documentation for [`Into`]. | |
9e0c209e SL |
382 | /// |
383 | /// [`TryFrom`]: trait.TryFrom.html | |
7cac9316 | 384 | /// [`Into`]: trait.Into.html |
a7813a04 XL |
385 | #[unstable(feature = "try_from", issue = "33417")] |
386 | pub trait TryInto<T>: Sized { | |
387 | /// The type returned in the event of a conversion error. | |
cc61c64b | 388 | type Error; |
a7813a04 XL |
389 | |
390 | /// Performs the conversion. | |
cc61c64b | 391 | fn try_into(self) -> Result<T, Self::Error>; |
a7813a04 XL |
392 | } |
393 | ||
394 | /// Attempt to construct `Self` via a conversion. | |
395 | #[unstable(feature = "try_from", issue = "33417")] | |
396 | pub trait TryFrom<T>: Sized { | |
397 | /// The type returned in the event of a conversion error. | |
cc61c64b | 398 | type Error; |
a7813a04 XL |
399 | |
400 | /// Performs the conversion. | |
cc61c64b | 401 | fn try_from(value: T) -> Result<Self, Self::Error>; |
a7813a04 XL |
402 | } |
403 | ||
c34b1796 AL |
404 | //////////////////////////////////////////////////////////////////////////////// |
405 | // GENERIC IMPLS | |
406 | //////////////////////////////////////////////////////////////////////////////// | |
407 | ||
408 | // As lifts over & | |
409 | #[stable(feature = "rust1", since = "1.0.0")] | |
0bf4aa26 | 410 | impl<T: ?Sized, U: ?Sized> AsRef<U> for &T where T: AsRef<U> |
cc61c64b | 411 | { |
c34b1796 AL |
412 | fn as_ref(&self) -> &U { |
413 | <T as AsRef<U>>::as_ref(*self) | |
414 | } | |
415 | } | |
416 | ||
417 | // As lifts over &mut | |
418 | #[stable(feature = "rust1", since = "1.0.0")] | |
0bf4aa26 | 419 | impl<T: ?Sized, U: ?Sized> AsRef<U> for &mut T where T: AsRef<U> |
cc61c64b | 420 | { |
c34b1796 AL |
421 | fn as_ref(&self) -> &U { |
422 | <T as AsRef<U>>::as_ref(*self) | |
423 | } | |
424 | } | |
425 | ||
0531ce1d | 426 | // FIXME (#45742): replace the above impls for &/&mut with the following more general one: |
c34b1796 AL |
427 | // // As lifts over Deref |
428 | // impl<D: ?Sized + Deref, U: ?Sized> AsRef<U> for D where D::Target: AsRef<U> { | |
429 | // fn as_ref(&self) -> &U { | |
430 | // self.deref().as_ref() | |
431 | // } | |
432 | // } | |
433 | ||
434 | // AsMut lifts over &mut | |
435 | #[stable(feature = "rust1", since = "1.0.0")] | |
0bf4aa26 | 436 | impl<T: ?Sized, U: ?Sized> AsMut<U> for &mut T where T: AsMut<U> |
cc61c64b | 437 | { |
c34b1796 AL |
438 | fn as_mut(&mut self) -> &mut U { |
439 | (*self).as_mut() | |
440 | } | |
441 | } | |
442 | ||
0531ce1d | 443 | // FIXME (#45742): replace the above impl for &mut with the following more general one: |
c34b1796 AL |
444 | // // AsMut lifts over DerefMut |
445 | // impl<D: ?Sized + Deref, U: ?Sized> AsMut<U> for D where D::Target: AsMut<U> { | |
446 | // fn as_mut(&mut self) -> &mut U { | |
447 | // self.deref_mut().as_mut() | |
448 | // } | |
449 | // } | |
450 | ||
451 | // From implies Into | |
452 | #[stable(feature = "rust1", since = "1.0.0")] | |
cc61c64b XL |
453 | impl<T, U> Into<U> for T where U: From<T> |
454 | { | |
c34b1796 AL |
455 | fn into(self) -> U { |
456 | U::from(self) | |
457 | } | |
458 | } | |
459 | ||
460 | // From (and thus Into) is reflexive | |
461 | #[stable(feature = "rust1", since = "1.0.0")] | |
462 | impl<T> From<T> for T { | |
463 | fn from(t: T) -> T { t } | |
464 | } | |
465 | ||
a7813a04 XL |
466 | |
467 | // TryFrom implies TryInto | |
468 | #[unstable(feature = "try_from", issue = "33417")] | |
cc61c64b XL |
469 | impl<T, U> TryInto<U> for T where U: TryFrom<T> |
470 | { | |
471 | type Error = U::Error; | |
a7813a04 | 472 | |
cc61c64b | 473 | fn try_into(self) -> Result<U, U::Error> { |
a7813a04 XL |
474 | U::try_from(self) |
475 | } | |
476 | } | |
477 | ||
ea8adc8c XL |
478 | // Infallible conversions are semantically equivalent to fallible conversions |
479 | // with an uninhabited error type. | |
480 | #[unstable(feature = "try_from", issue = "33417")] | |
481 | impl<T, U> TryFrom<U> for T where T: From<U> { | |
0531ce1d | 482 | type Error = !; |
ea8adc8c XL |
483 | |
484 | fn try_from(value: U) -> Result<Self, Self::Error> { | |
485 | Ok(T::from(value)) | |
486 | } | |
487 | } | |
488 | ||
c34b1796 AL |
489 | //////////////////////////////////////////////////////////////////////////////// |
490 | // CONCRETE IMPLS | |
491 | //////////////////////////////////////////////////////////////////////////////// | |
492 | ||
493 | #[stable(feature = "rust1", since = "1.0.0")] | |
494 | impl<T> AsRef<[T]> for [T] { | |
495 | fn as_ref(&self) -> &[T] { | |
496 | self | |
497 | } | |
498 | } | |
499 | ||
500 | #[stable(feature = "rust1", since = "1.0.0")] | |
501 | impl<T> AsMut<[T]> for [T] { | |
502 | fn as_mut(&mut self) -> &mut [T] { | |
503 | self | |
504 | } | |
505 | } | |
506 | ||
507 | #[stable(feature = "rust1", since = "1.0.0")] | |
508 | impl AsRef<str> for str { | |
d9579d0f | 509 | #[inline] |
c34b1796 AL |
510 | fn as_ref(&self) -> &str { |
511 | self | |
512 | } | |
513 | } |