src/libcore/clone.rs

   1 // Copyright 2012-2013 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 //! The `Clone` trait for types that cannot be 'implicitly copied'.
  12 //!
  13 //! In Rust, some simple types are "implicitly copyable" and when you
  14 //! assign them or pass them as arguments, the receiver will get a copy,
  15 //! leaving the original value in place. These types do not require
  16 //! allocation to copy and do not have finalizers (i.e. they do not
  17 //! contain owned boxes or implement `Drop`), so the compiler considers
  18 //! them cheap and safe to copy. For other types copies must be made
  19 //! explicitly, by convention implementing the `Clone` trait and calling
  20 //! the `clone` method.
  21 //!
  22 //! Basic usage example:
  23 //!
  24 //! ```
  25 //! let s = String::new(); // String type implements Clone
  26 //! let copy = s.clone(); // so we can clone it
  27 //! ```
  28 //!
  29 //! To easily implement the Clone trait, you can also use
  30 //! `#[derive(Clone)]`. Example:
  31 //!
  32 //! ```
  33 //! #[derive(Clone)] // we add the Clone trait to Morpheus struct
  34 //! struct Morpheus {
  35 //!    blue_pill: f32,
  36 //!    red_pill: i64,
  37 //! }
  38 //!
  39 //! fn main() {
  40 //!    let f = Morpheus { blue_pill: 0.0, red_pill: 0 };
  41 //!    let copy = f.clone(); // and now we can clone it!
  42 //! }
  43 //! ```
  44
  45 #![stable(feature = "rust1", since = "1.0.0")]
  46
  47 use marker::Sized;
  48
  49 /// A common trait for cloning an object.
  50 ///
  51 /// This trait can be used with `#[derive]`.
  52 ///
  53 /// Types that are `Copy` should have a trivial implementation of `Clone`. More formally:
  54 /// if `T: Copy`, `x: T`, and `y: &T`, then `let x = y.clone();` is equivalent to `let x = *y;`.
  55 /// Manual implementations should be careful to uphold this invariant; however, unsafe code
  56 /// must not rely on it to ensure memory safety.
  57 #[stable(feature = "rust1", since = "1.0.0")]
  58 pub trait Clone : Sized {
  59     /// Returns a copy of the value.
  60     ///
  61     /// # Examples
  62     ///
  63     /// ```
  64     /// let hello = "Hello"; // &str implements Clone
  65     ///
  66     /// assert_eq!("Hello", hello.clone());
  67     /// ```
  68     #[stable(feature = "rust1", since = "1.0.0")]
  69     fn clone(&self) -> Self;
  70
  71     /// Performs copy-assignment from `source`.
  72     ///
  73     /// `a.clone_from(&b)` is equivalent to `a = b.clone()` in functionality,
  74     /// but can be overridden to reuse the resources of `a` to avoid unnecessary
  75     /// allocations.
  76     #[inline(always)]
  77     #[stable(feature = "rust1", since = "1.0.0")]
  78     fn clone_from(&mut self, source: &Self) {
  79         *self = source.clone()
  80     }
  81 }
  82
  83 // FIXME(aburka): this method is used solely by #[derive] to
  84 // assert that every component of a type implements Clone.
  85 //
  86 // This should never be called by user code.
  87 #[doc(hidden)]
  88 #[inline(always)]
  89 #[unstable(feature = "derive_clone_copy",
  90            reason = "deriving hack, should not be public",
  91            issue = "0")]
  92 pub fn assert_receiver_is_clone<T: Clone + ?Sized>(_: &T) {}
  93
  94 #[stable(feature = "rust1", since = "1.0.0")]
  95 impl<'a, T: ?Sized> Clone for &'a T {
  96     /// Returns a shallow copy of the reference.
  97     #[inline]
  98     fn clone(&self) -> &'a T { *self }
  99 }
 100
 101 macro_rules! clone_impl {
 102     ($t:ty) => {
 103         #[stable(feature = "rust1", since = "1.0.0")]
 104         impl Clone for $t {
 105             /// Returns a deep copy of the value.
 106             #[inline]
 107             fn clone(&self) -> $t { *self }
 108         }
 109     }
 110 }
 111
 112 clone_impl! { isize }
 113 clone_impl! { i8 }
 114 clone_impl! { i16 }
 115 clone_impl! { i32 }
 116 clone_impl! { i64 }
 117
 118 clone_impl! { usize }
 119 clone_impl! { u8 }
 120 clone_impl! { u16 }
 121 clone_impl! { u32 }
 122 clone_impl! { u64 }
 123
 124 clone_impl! { f32 }
 125 clone_impl! { f64 }
 126
 127 clone_impl! { () }
 128 clone_impl! { bool }
 129 clone_impl! { char }