72a25d05bf
This updates the standard library's documentation to use the new syntax. The documentation is worthwhile to update as it should be more idiomatic (particularly for features like this, which are nice for users to get acquainted with). The general codebase is likely more hassle than benefit to update: it'll hurt git blame, and generally updates can be done by folks updating the code if (and when) that makes things more readable with the new format. A few places in the compiler and library code are updated (mostly just due to already having been done when this commit was first authored).
496 lines
14 KiB
Rust
496 lines
14 KiB
Rust
//! A module for working with borrowed data.
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#![stable(feature = "rust1", since = "1.0.0")]
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use core::cmp::Ordering;
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use core::hash::{Hash, Hasher};
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use core::ops::Deref;
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#[cfg(not(no_global_oom_handling))]
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use core::ops::{Add, AddAssign};
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#[stable(feature = "rust1", since = "1.0.0")]
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pub use core::borrow::{Borrow, BorrowMut};
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use crate::fmt;
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#[cfg(not(no_global_oom_handling))]
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use crate::string::String;
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use Cow::*;
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
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where
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B: ToOwned,
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<B as ToOwned>::Owned: 'a,
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{
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fn borrow(&self) -> &B {
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&**self
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}
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}
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/// A generalization of `Clone` to borrowed data.
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///
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/// Some types make it possible to go from borrowed to owned, usually by
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/// implementing the `Clone` trait. But `Clone` works only for going from `&T`
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/// to `T`. The `ToOwned` trait generalizes `Clone` to construct owned data
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/// from any borrow of a given type.
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#[cfg_attr(not(test), rustc_diagnostic_item = "ToOwned")]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait ToOwned {
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/// The resulting type after obtaining ownership.
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#[stable(feature = "rust1", since = "1.0.0")]
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type Owned: Borrow<Self>;
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/// Creates owned data from borrowed data, usually by cloning.
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// let s: &str = "a";
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/// let ss: String = s.to_owned();
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///
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/// let v: &[i32] = &[1, 2];
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/// let vv: Vec<i32> = v.to_owned();
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[must_use = "cloning is often expensive and is not expected to have side effects"]
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fn to_owned(&self) -> Self::Owned;
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/// Uses borrowed data to replace owned data, usually by cloning.
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///
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/// This is borrow-generalized version of `Clone::clone_from`.
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///
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/// # Examples
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///
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/// Basic usage:
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///
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/// ```
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/// # #![feature(toowned_clone_into)]
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/// let mut s: String = String::new();
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/// "hello".clone_into(&mut s);
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///
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/// let mut v: Vec<i32> = Vec::new();
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/// [1, 2][..].clone_into(&mut v);
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/// ```
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#[unstable(feature = "toowned_clone_into", reason = "recently added", issue = "41263")]
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fn clone_into(&self, target: &mut Self::Owned) {
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*target = self.to_owned();
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T> ToOwned for T
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where
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T: Clone,
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{
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type Owned = T;
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fn to_owned(&self) -> T {
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self.clone()
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}
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fn clone_into(&self, target: &mut T) {
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target.clone_from(self);
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}
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}
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/// A clone-on-write smart pointer.
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///
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/// The type `Cow` is a smart pointer providing clone-on-write functionality: it
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/// can enclose and provide immutable access to borrowed data, and clone the
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/// data lazily when mutation or ownership is required. The type is designed to
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/// work with general borrowed data via the `Borrow` trait.
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///
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/// `Cow` implements `Deref`, which means that you can call
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/// non-mutating methods directly on the data it encloses. If mutation
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/// is desired, `to_mut` will obtain a mutable reference to an owned
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/// value, cloning if necessary.
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///
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/// If you need reference-counting pointers, note that
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/// [`Rc::make_mut`][crate::rc::Rc::make_mut] and
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/// [`Arc::make_mut`][crate::sync::Arc::make_mut] can provide clone-on-write
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/// functionality as well.
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///
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/// # Examples
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///
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/// ```
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/// use std::borrow::Cow;
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///
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/// fn abs_all(input: &mut Cow<[i32]>) {
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/// for i in 0..input.len() {
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/// let v = input[i];
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/// if v < 0 {
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/// // Clones into a vector if not already owned.
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/// input.to_mut()[i] = -v;
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/// }
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/// }
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/// }
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///
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/// // No clone occurs because `input` doesn't need to be mutated.
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/// let slice = [0, 1, 2];
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/// let mut input = Cow::from(&slice[..]);
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/// abs_all(&mut input);
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///
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/// // Clone occurs because `input` needs to be mutated.
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/// let slice = [-1, 0, 1];
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/// let mut input = Cow::from(&slice[..]);
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/// abs_all(&mut input);
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///
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/// // No clone occurs because `input` is already owned.
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/// let mut input = Cow::from(vec![-1, 0, 1]);
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/// abs_all(&mut input);
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/// ```
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///
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/// Another example showing how to keep `Cow` in a struct:
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///
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/// ```
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/// use std::borrow::Cow;
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///
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/// struct Items<'a, X: 'a> where [X]: ToOwned<Owned = Vec<X>> {
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/// values: Cow<'a, [X]>,
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/// }
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///
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/// impl<'a, X: Clone + 'a> Items<'a, X> where [X]: ToOwned<Owned = Vec<X>> {
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/// fn new(v: Cow<'a, [X]>) -> Self {
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/// Items { values: v }
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/// }
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/// }
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///
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/// // Creates a container from borrowed values of a slice
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/// let readonly = [1, 2];
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/// let borrowed = Items::new((&readonly[..]).into());
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/// match borrowed {
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/// Items { values: Cow::Borrowed(b) } => println!("borrowed {b:?}"),
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/// _ => panic!("expect borrowed value"),
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/// }
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///
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/// let mut clone_on_write = borrowed;
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/// // Mutates the data from slice into owned vec and pushes a new value on top
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/// clone_on_write.values.to_mut().push(3);
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/// println!("clone_on_write = {:?}", clone_on_write.values);
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///
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/// // The data was mutated. Let's check it out.
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/// match clone_on_write {
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/// Items { values: Cow::Owned(_) } => println!("clone_on_write contains owned data"),
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/// _ => panic!("expect owned data"),
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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#[cfg_attr(not(test), rustc_diagnostic_item = "Cow")]
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pub enum Cow<'a, B: ?Sized + 'a>
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where
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B: ToOwned,
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{
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/// Borrowed data.
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#[stable(feature = "rust1", since = "1.0.0")]
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Borrowed(#[stable(feature = "rust1", since = "1.0.0")] &'a B),
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/// Owned data.
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#[stable(feature = "rust1", since = "1.0.0")]
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Owned(#[stable(feature = "rust1", since = "1.0.0")] <B as ToOwned>::Owned),
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B: ?Sized + ToOwned> Clone for Cow<'_, B> {
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fn clone(&self) -> Self {
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match *self {
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Borrowed(b) => Borrowed(b),
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Owned(ref o) => {
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let b: &B = o.borrow();
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Owned(b.to_owned())
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}
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}
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}
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fn clone_from(&mut self, source: &Self) {
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match (self, source) {
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(&mut Owned(ref mut dest), &Owned(ref o)) => o.borrow().clone_into(dest),
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(t, s) => *t = s.clone(),
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}
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}
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}
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impl<B: ?Sized + ToOwned> Cow<'_, B> {
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/// Returns true if the data is borrowed, i.e. if `to_mut` would require additional work.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(cow_is_borrowed)]
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/// use std::borrow::Cow;
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///
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/// let cow = Cow::Borrowed("moo");
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/// assert!(cow.is_borrowed());
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///
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/// let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string());
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/// assert!(!bull.is_borrowed());
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/// ```
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#[unstable(feature = "cow_is_borrowed", issue = "65143")]
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#[rustc_const_unstable(feature = "const_cow_is_borrowed", issue = "65143")]
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pub const fn is_borrowed(&self) -> bool {
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match *self {
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Borrowed(_) => true,
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Owned(_) => false,
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}
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}
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/// Returns true if the data is owned, i.e. if `to_mut` would be a no-op.
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///
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/// # Examples
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///
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/// ```
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/// #![feature(cow_is_borrowed)]
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/// use std::borrow::Cow;
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///
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/// let cow: Cow<'_, str> = Cow::Owned("moo".to_string());
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/// assert!(cow.is_owned());
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///
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/// let bull = Cow::Borrowed("...moo?");
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/// assert!(!bull.is_owned());
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/// ```
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#[unstable(feature = "cow_is_borrowed", issue = "65143")]
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#[rustc_const_unstable(feature = "const_cow_is_borrowed", issue = "65143")]
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pub const fn is_owned(&self) -> bool {
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!self.is_borrowed()
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}
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/// Acquires a mutable reference to the owned form of the data.
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///
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/// Clones the data if it is not already owned.
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///
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/// # Examples
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///
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/// ```
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/// use std::borrow::Cow;
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///
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/// let mut cow = Cow::Borrowed("foo");
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/// cow.to_mut().make_ascii_uppercase();
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///
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/// assert_eq!(
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/// cow,
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/// Cow::Owned(String::from("FOO")) as Cow<str>
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/// );
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn to_mut(&mut self) -> &mut <B as ToOwned>::Owned {
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match *self {
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Borrowed(borrowed) => {
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*self = Owned(borrowed.to_owned());
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match *self {
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Borrowed(..) => unreachable!(),
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Owned(ref mut owned) => owned,
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}
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}
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Owned(ref mut owned) => owned,
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}
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}
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/// Extracts the owned data.
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///
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/// Clones the data if it is not already owned.
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///
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/// # Examples
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///
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/// Calling `into_owned` on a `Cow::Borrowed` clones the underlying data
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/// and becomes a `Cow::Owned`:
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///
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/// ```
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/// use std::borrow::Cow;
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///
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/// let s = "Hello world!";
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/// let cow = Cow::Borrowed(s);
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///
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/// assert_eq!(
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/// cow.into_owned(),
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/// String::from(s)
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/// );
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/// ```
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///
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/// Calling `into_owned` on a `Cow::Owned` is a no-op:
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///
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/// ```
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/// use std::borrow::Cow;
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///
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/// let s = "Hello world!";
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/// let cow: Cow<str> = Cow::Owned(String::from(s));
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///
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/// assert_eq!(
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/// cow.into_owned(),
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/// String::from(s)
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/// );
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn into_owned(self) -> <B as ToOwned>::Owned {
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match self {
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Borrowed(borrowed) => borrowed.to_owned(),
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Owned(owned) => owned,
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}
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_const_unstable(feature = "const_deref", issue = "88955")]
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impl<B: ?Sized + ToOwned> const Deref for Cow<'_, B>
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where
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B::Owned: ~const Borrow<B>,
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{
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type Target = B;
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fn deref(&self) -> &B {
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match *self {
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Borrowed(borrowed) => borrowed,
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Owned(ref owned) => owned.borrow(),
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}
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B: ?Sized> Eq for Cow<'_, B> where B: Eq + ToOwned {}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B: ?Sized> Ord for Cow<'_, B>
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where
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B: Ord + ToOwned,
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{
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#[inline]
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fn cmp(&self, other: &Self) -> Ordering {
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Ord::cmp(&**self, &**other)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, 'b, B: ?Sized, C: ?Sized> PartialEq<Cow<'b, C>> for Cow<'a, B>
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where
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B: PartialEq<C> + ToOwned,
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C: ToOwned,
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{
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#[inline]
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fn eq(&self, other: &Cow<'b, C>) -> bool {
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PartialEq::eq(&**self, &**other)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, B: ?Sized> PartialOrd for Cow<'a, B>
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where
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B: PartialOrd + ToOwned,
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{
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#[inline]
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fn partial_cmp(&self, other: &Cow<'a, B>) -> Option<Ordering> {
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PartialOrd::partial_cmp(&**self, &**other)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B: ?Sized> fmt::Debug for Cow<'_, B>
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where
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B: fmt::Debug + ToOwned<Owned: fmt::Debug>,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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match *self {
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Borrowed(ref b) => fmt::Debug::fmt(b, f),
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Owned(ref o) => fmt::Debug::fmt(o, f),
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}
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B: ?Sized> fmt::Display for Cow<'_, B>
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where
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B: fmt::Display + ToOwned<Owned: fmt::Display>,
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{
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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match *self {
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Borrowed(ref b) => fmt::Display::fmt(b, f),
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Owned(ref o) => fmt::Display::fmt(o, f),
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}
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}
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}
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#[stable(feature = "default", since = "1.11.0")]
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impl<B: ?Sized> Default for Cow<'_, B>
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where
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B: ToOwned<Owned: Default>,
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{
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/// Creates an owned Cow<'a, B> with the default value for the contained owned value.
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fn default() -> Self {
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Owned(<B as ToOwned>::Owned::default())
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<B: ?Sized> Hash for Cow<'_, B>
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where
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B: Hash + ToOwned,
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{
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#[inline]
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fn hash<H: Hasher>(&self, state: &mut H) {
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Hash::hash(&**self, state)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T> {
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fn as_ref(&self) -> &T {
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self
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}
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}
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "cow_add", since = "1.14.0")]
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impl<'a> Add<&'a str> for Cow<'a, str> {
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type Output = Cow<'a, str>;
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#[inline]
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fn add(mut self, rhs: &'a str) -> Self::Output {
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self += rhs;
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self
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}
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}
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "cow_add", since = "1.14.0")]
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impl<'a> Add<Cow<'a, str>> for Cow<'a, str> {
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type Output = Cow<'a, str>;
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#[inline]
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fn add(mut self, rhs: Cow<'a, str>) -> Self::Output {
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self += rhs;
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self
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}
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}
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "cow_add", since = "1.14.0")]
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impl<'a> AddAssign<&'a str> for Cow<'a, str> {
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fn add_assign(&mut self, rhs: &'a str) {
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if self.is_empty() {
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*self = Cow::Borrowed(rhs)
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} else if !rhs.is_empty() {
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if let Cow::Borrowed(lhs) = *self {
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let mut s = String::with_capacity(lhs.len() + rhs.len());
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s.push_str(lhs);
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*self = Cow::Owned(s);
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}
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self.to_mut().push_str(rhs);
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}
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}
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}
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#[cfg(not(no_global_oom_handling))]
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#[stable(feature = "cow_add", since = "1.14.0")]
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impl<'a> AddAssign<Cow<'a, str>> for Cow<'a, str> {
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fn add_assign(&mut self, rhs: Cow<'a, str>) {
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if self.is_empty() {
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*self = rhs
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} else if !rhs.is_empty() {
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if let Cow::Borrowed(lhs) = *self {
|
|
let mut s = String::with_capacity(lhs.len() + rhs.len());
|
|
s.push_str(lhs);
|
|
*self = Cow::Owned(s);
|
|
}
|
|
self.to_mut().push_str(&rhs);
|
|
}
|
|
}
|
|
}
|