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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 #[stable(feature = "rust1", since = "1.0.0")]
53 pub trait Clone : Sized {
54 /// Returns a copy of the value.
55 ///
56 /// # Examples
57 ///
58 /// ```
59 /// let hello = "Hello"; // &str implements Clone
60 ///
61 /// assert_eq!("Hello", hello.clone());
62 /// ```
63 #[stable(feature = "rust1", since = "1.0.0")]
64 fn clone(&self) -> Self;
65
66 /// Performs copy-assignment from `source`.
67 ///
68 /// `a.clone_from(&b)` is equivalent to `a = b.clone()` in functionality,
69 /// but can be overridden to reuse the resources of `a` to avoid unnecessary
70 /// allocations.
71 #[inline(always)]
72 #[stable(feature = "rust1", since = "1.0.0")]
73 fn clone_from(&mut self, source: &Self) {
74 *self = source.clone()
75 }
76 }
77
78 #[stable(feature = "rust1", since = "1.0.0")]
79 impl<'a, T: ?Sized> Clone for &'a T {
80 /// Returns a shallow copy of the reference.
81 #[inline]
82 fn clone(&self) -> &'a T { *self }
83 }
84
85 macro_rules! clone_impl {
86 ($t:ty) => {
87 #[stable(feature = "rust1", since = "1.0.0")]
88 impl Clone for $t {
89 /// Returns a deep copy of the value.
90 #[inline]
91 fn clone(&self) -> $t { *self }
92 }
93 }
94 }
95
96 clone_impl! { isize }
97 clone_impl! { i8 }
98 clone_impl! { i16 }
99 clone_impl! { i32 }
100 clone_impl! { i64 }
101
102 clone_impl! { usize }
103 clone_impl! { u8 }
104 clone_impl! { u16 }
105 clone_impl! { u32 }
106 clone_impl! { u64 }
107
108 clone_impl! { f32 }
109 clone_impl! { f64 }
110
111 clone_impl! { () }
112 clone_impl! { bool }
113 clone_impl! { char }