c5aa879490
Adds documentation to Clone, specifying that Copy types should have a trivial Clone impl. Fixes #33416.
130 lines
3.9 KiB
Rust
130 lines
3.9 KiB
Rust
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! The `Clone` trait for types that cannot be 'implicitly copied'.
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//!
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//! In Rust, some simple types are "implicitly copyable" and when you
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//! assign them or pass them as arguments, the receiver will get a copy,
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//! leaving the original value in place. These types do not require
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//! allocation to copy and do not have finalizers (i.e. they do not
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//! contain owned boxes or implement `Drop`), so the compiler considers
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//! them cheap and safe to copy. For other types copies must be made
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//! explicitly, by convention implementing the `Clone` trait and calling
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//! the `clone` method.
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//!
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//! Basic usage example:
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//!
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//! ```
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//! let s = String::new(); // String type implements Clone
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//! let copy = s.clone(); // so we can clone it
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//! ```
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//!
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//! To easily implement the Clone trait, you can also use
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//! `#[derive(Clone)]`. Example:
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//!
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//! ```
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//! #[derive(Clone)] // we add the Clone trait to Morpheus struct
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//! struct Morpheus {
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//! blue_pill: f32,
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//! red_pill: i64,
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//! }
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//!
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//! fn main() {
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//! let f = Morpheus { blue_pill: 0.0, red_pill: 0 };
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//! let copy = f.clone(); // and now we can clone it!
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//! }
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//! ```
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#![stable(feature = "rust1", since = "1.0.0")]
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use marker::Sized;
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/// A common trait for cloning an object.
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///
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/// This trait can be used with `#[derive]`.
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///
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/// Types that are `Copy` should have a trivial implementation of `Clone`. More formally:
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/// if `T: Copy`, `x: T`, and `y: &T`, then `let x = y.clone();` is equivalent to `let x = *y;`.
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/// Manual implementations should be careful to uphold this invariant; however, unsafe code
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/// must not rely on it to ensure memory safety.
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait Clone : Sized {
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/// Returns a copy of the value.
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///
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/// # Examples
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///
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/// ```
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/// let hello = "Hello"; // &str implements Clone
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///
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/// assert_eq!("Hello", hello.clone());
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn clone(&self) -> Self;
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/// Performs copy-assignment from `source`.
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///
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/// `a.clone_from(&b)` is equivalent to `a = b.clone()` in functionality,
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/// but can be overridden to reuse the resources of `a` to avoid unnecessary
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/// allocations.
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#[inline(always)]
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#[stable(feature = "rust1", since = "1.0.0")]
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fn clone_from(&mut self, source: &Self) {
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*self = source.clone()
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}
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}
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// FIXME(aburka): this method is used solely by #[derive] to
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// assert that every component of a type implements Clone.
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//
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// This should never be called by user code.
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#[doc(hidden)]
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#[inline(always)]
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#[unstable(feature = "derive_clone_copy",
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reason = "deriving hack, should not be public",
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issue = "0")]
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pub fn assert_receiver_is_clone<T: Clone + ?Sized>(_: &T) {}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, T: ?Sized> Clone for &'a T {
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/// Returns a shallow copy of the reference.
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#[inline]
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fn clone(&self) -> &'a T { *self }
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}
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macro_rules! clone_impl {
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($t:ty) => {
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Clone for $t {
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/// Returns a deep copy of the value.
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#[inline]
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fn clone(&self) -> $t { *self }
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}
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}
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}
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clone_impl! { isize }
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clone_impl! { i8 }
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clone_impl! { i16 }
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clone_impl! { i32 }
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clone_impl! { i64 }
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clone_impl! { usize }
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clone_impl! { u8 }
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clone_impl! { u16 }
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clone_impl! { u32 }
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clone_impl! { u64 }
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clone_impl! { f32 }
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clone_impl! { f64 }
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clone_impl! { () }
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clone_impl! { bool }
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clone_impl! { char }
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