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.
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.
11 //! A module for working with borrowed data.
13 #![stable(feature = "rust1", since = "1.0.0")]
15 use core::cmp::Ordering;
16 use core::hash::{Hash, Hasher};
17 use core::ops::{Add, AddAssign, Deref};
24 #[stable(feature = "rust1", since = "1.0.0")]
25 pub use core::borrow::{Borrow, BorrowMut};
27 #[stable(feature = "rust1", since = "1.0.0")]
28 impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
30 <B as ToOwned>::Owned: 'a
32 fn borrow(&self) -> &B {
37 /// A generalization of `Clone` to borrowed data.
39 /// Some types make it possible to go from borrowed to owned, usually by
40 /// implementing the `Clone` trait. But `Clone` works only for going from `&T`
41 /// to `T`. The `ToOwned` trait generalizes `Clone` to construct owned data
42 /// from any borrow of a given type.
43 #[stable(feature = "rust1", since = "1.0.0")]
45 #[stable(feature = "rust1", since = "1.0.0")]
46 type Owned: Borrow<Self>;
48 /// Creates owned data from borrowed data, usually by cloning.
55 /// let s: &str = "a";
56 /// let ss: String = s.to_owned();
58 /// let v: &[i32] = &[1, 2];
59 /// let vv: Vec<i32> = v.to_owned();
61 #[stable(feature = "rust1", since = "1.0.0")]
62 fn to_owned(&self) -> Self::Owned;
64 /// Uses borrowed data to replace owned data, usually by cloning.
66 /// This is borrow-generalized version of `Clone::clone_from`.
73 /// # #![feature(toowned_clone_into)]
74 /// let mut s: String = String::new();
75 /// "hello".clone_into(&mut s);
77 /// let mut v: Vec<i32> = Vec::new();
78 /// [1, 2][..].clone_into(&mut v);
80 #[unstable(feature = "toowned_clone_into",
81 reason = "recently added",
83 fn clone_into(&self, target: &mut Self::Owned) {
84 *target = self.to_owned();
88 #[stable(feature = "rust1", since = "1.0.0")]
93 fn to_owned(&self) -> T {
97 fn clone_into(&self, target: &mut T) {
98 target.clone_from(self);
102 /// A clone-on-write smart pointer.
104 /// The type `Cow` is a smart pointer providing clone-on-write functionality: it
105 /// can enclose and provide immutable access to borrowed data, and clone the
106 /// data lazily when mutation or ownership is required. The type is designed to
107 /// work with general borrowed data via the `Borrow` trait.
109 /// `Cow` implements `Deref`, which means that you can call
110 /// non-mutating methods directly on the data it encloses. If mutation
111 /// is desired, `to_mut` will obtain a mutable reference to an owned
112 /// value, cloning if necessary.
117 /// use std::borrow::Cow;
119 /// fn abs_all(input: &mut Cow<[i32]>) {
120 /// for i in 0..input.len() {
121 /// let v = input[i];
123 /// // Clones into a vector if not already owned.
124 /// input.to_mut()[i] = -v;
129 /// // No clone occurs because `input` doesn't need to be mutated.
130 /// let slice = [0, 1, 2];
131 /// let mut input = Cow::from(&slice[..]);
132 /// abs_all(&mut input);
134 /// // Clone occurs because `input` needs to be mutated.
135 /// let slice = [-1, 0, 1];
136 /// let mut input = Cow::from(&slice[..]);
137 /// abs_all(&mut input);
139 /// // No clone occurs because `input` is already owned.
140 /// let mut input = Cow::from(vec![-1, 0, 1]);
141 /// abs_all(&mut input);
143 #[stable(feature = "rust1", since = "1.0.0")]
144 pub enum Cow<'a, B: ?Sized + 'a>
148 #[stable(feature = "rust1", since = "1.0.0")]
149 Borrowed(#[stable(feature = "rust1", since = "1.0.0")]
153 #[stable(feature = "rust1", since = "1.0.0")]
154 Owned(#[stable(feature = "rust1", since = "1.0.0")]
155 <B as ToOwned>::Owned),
158 #[stable(feature = "rust1", since = "1.0.0")]
159 impl<'a, B: ?Sized> Clone for Cow<'a, B>
162 fn clone(&self) -> Cow<'a, B> {
164 Borrowed(b) => Borrowed(b),
166 let b: &B = o.borrow();
172 fn clone_from(&mut self, source: &Cow<'a, B>) {
173 if let Owned(ref mut dest) = *self {
174 if let Owned(ref o) = *source {
175 o.borrow().clone_into(dest);
180 *self = source.clone();
184 impl<'a, B: ?Sized> Cow<'a, B>
187 /// Acquires a mutable reference to the owned form of the data.
189 /// Clones the data if it is not already owned.
194 /// use std::ascii::AsciiExt;
195 /// use std::borrow::Cow;
197 /// let mut cow = Cow::Borrowed("foo");
198 /// cow.to_mut().make_ascii_uppercase();
202 /// Cow::Owned(String::from("FOO")) as Cow<str>
205 #[stable(feature = "rust1", since = "1.0.0")]
206 pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned {
208 Borrowed(borrowed) => {
209 *self = Owned(borrowed.to_owned());
211 Borrowed(..) => unreachable!(),
212 Owned(ref mut owned) => owned,
215 Owned(ref mut owned) => owned,
219 /// Extracts the owned data.
221 /// Clones the data if it is not already owned.
225 /// Calling `into_owned` on a `Cow::Borrowed` clones the underlying data
226 /// and becomes a `Cow::Owned`:
229 /// use std::borrow::Cow;
231 /// let s = "Hello world!";
232 /// let cow = Cow::Borrowed(s);
235 /// cow.into_owned(),
236 /// Cow::Owned(String::from(s))
240 /// Calling `into_owned` on a `Cow::Owned` is a no-op:
243 /// use std::borrow::Cow;
245 /// let s = "Hello world!";
246 /// let cow: Cow<str> = Cow::Owned(String::from(s));
249 /// cow.into_owned(),
250 /// Cow::Owned(String::from(s))
253 #[stable(feature = "rust1", since = "1.0.0")]
254 pub fn into_owned(self) -> <B as ToOwned>::Owned {
256 Borrowed(borrowed) => borrowed.to_owned(),
257 Owned(owned) => owned,
262 #[stable(feature = "rust1", since = "1.0.0")]
263 impl<'a, B: ?Sized> Deref for Cow<'a, B>
268 fn deref(&self) -> &B {
270 Borrowed(borrowed) => borrowed,
271 Owned(ref owned) => owned.borrow(),
276 #[stable(feature = "rust1", since = "1.0.0")]
277 impl<'a, B: ?Sized> Eq for Cow<'a, B> where B: Eq + ToOwned {}
279 #[stable(feature = "rust1", since = "1.0.0")]
280 impl<'a, B: ?Sized> Ord for Cow<'a, B>
281 where B: Ord + ToOwned
284 fn cmp(&self, other: &Cow<'a, B>) -> Ordering {
285 Ord::cmp(&**self, &**other)
289 #[stable(feature = "rust1", since = "1.0.0")]
290 impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B>
291 where B: PartialEq<C> + ToOwned,
295 fn eq(&self, other: &Cow<'b, C>) -> bool {
296 PartialEq::eq(&**self, &**other)
300 #[stable(feature = "rust1", since = "1.0.0")]
301 impl<'a, B: ?Sized> PartialOrd for Cow<'a, B>
302 where B: PartialOrd + ToOwned
305 fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering> {
306 PartialOrd::partial_cmp(&**self, &**other)
310 #[stable(feature = "rust1", since = "1.0.0")]
311 impl<'a, B: ?Sized> fmt::Debug for Cow<'a, B>
312 where B: fmt::Debug + ToOwned,
313 <B as ToOwned>::Owned: fmt::Debug
315 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
317 Borrowed(ref b) => fmt::Debug::fmt(b, f),
318 Owned(ref o) => fmt::Debug::fmt(o, f),
323 #[stable(feature = "rust1", since = "1.0.0")]
324 impl<'a, B: ?Sized> fmt::Display for Cow<'a, B>
325 where B: fmt::Display + ToOwned,
326 <B as ToOwned>::Owned: fmt::Display
328 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
330 Borrowed(ref b) => fmt::Display::fmt(b, f),
331 Owned(ref o) => fmt::Display::fmt(o, f),
336 #[stable(feature = "default", since = "1.11.0")]
337 impl<'a, B: ?Sized> Default for Cow<'a, B>
339 <B as ToOwned>::Owned: Default
341 /// Creates an owned Cow<'a, B> with the default value for the contained owned value.
342 fn default() -> Cow<'a, B> {
343 Owned(<B as ToOwned>::Owned::default())
347 #[stable(feature = "rust1", since = "1.0.0")]
348 impl<'a, B: ?Sized> Hash for Cow<'a, B>
349 where B: Hash + ToOwned
352 fn hash<H: Hasher>(&self, state: &mut H) {
353 Hash::hash(&**self, state)
357 #[stable(feature = "rust1", since = "1.0.0")]
359 impl<'a, T: ?Sized + ToOwned> AsRef<T> for Cow<'a, T> {
360 fn as_ref(&self) -> &T {
365 #[stable(feature = "cow_add", since = "1.14.0")]
366 impl<'a> Add<&'a str> for Cow<'a, str> {
367 type Output = Cow<'a, str>;
370 fn add(mut self, rhs: &'a str) -> Self::Output {
376 #[stable(feature = "cow_add", since = "1.14.0")]
377 impl<'a> Add<Cow<'a, str>> for Cow<'a, str> {
378 type Output = Cow<'a, str>;
381 fn add(mut self, rhs: Cow<'a, str>) -> Self::Output {
387 #[stable(feature = "cow_add", since = "1.14.0")]
388 impl<'a> AddAssign<&'a str> for Cow<'a, str> {
389 fn add_assign(&mut self, rhs: &'a str) {
391 *self = Cow::Borrowed(rhs)
392 } else if rhs.is_empty() {
395 if let Cow::Borrowed(lhs) = *self {
396 let mut s = String::with_capacity(lhs.len() + rhs.len());
398 *self = Cow::Owned(s);
400 self.to_mut().push_str(rhs);
405 #[stable(feature = "cow_add", since = "1.14.0")]
406 impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str> {
407 fn add_assign(&mut self, rhs: Cow<'a, str>) {
410 } else if rhs.is_empty() {
413 if let Cow::Borrowed(lhs) = *self {
414 let mut s = String::with_capacity(lhs.len() + rhs.len());
416 *self = Cow::Owned(s);
418 self.to_mut().push_str(&rhs);