      1
      2
      3
      4
      5
      6
      7
      8
      9
     10
     11
     12
     13
     14
     15
     16
     17
     18
     19
     20
     21
     22
     23
     24
     25
     26
     27
     28
     29
     30
     31
     32
     33
     34
     35
     36
     37
     38
     39
     40
     41
     42
     43
     44
     45
     46
     47
     48
     49
     50
     51
     52
     53
     54
     55
     56
     57
     58
     59
     60
     61
     62
     63
     64
     65
     66
     67
     68
     69
     70
     71
     72
     73
     74
     75
     76
     77
     78
     79
     80
     81
     82
     83
     84
     85
     86
     87
     88
     89
     90
     91
     92
     93
     94
     95
     96
     97
     98
     99
    100
    101
    102
    103
    104
    105
    106
    107
    108
    109
    110
    111
    112
    113
    114
    115
    116
    117
    118
    119
    120
    121
    122
    123
    124
    125
    126
    127
    128
    129
    130
    131
    132
    133
    134
    135
    136
    137
    138
    139
    140
    141
    142
    143
    144
    145
    146
    147
    148
    149
    150
    151
    152
    153
    154
    155
    156
    157

    // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    //! The `Clone` trait for types that cannot be 'implicitly copied'.
    //!
    //! In Rust, some simple types are "implicitly copyable" and when you
    //! assign them or pass them as arguments, the receiver will get a copy,
    //! leaving the original value in place. These types do not require
    //! allocation to copy and do not have finalizers (i.e. they do not
    //! contain owned boxes or implement `Drop`), so the compiler considers
    //! them cheap and safe to copy. For other types copies must be made
    //! explicitly, by convention implementing the `Clone` trait and calling
    //! the `clone` method.
    //!
    //! Basic usage example:
    //!
    //! ```
    //! let s = String::new(); // String type implements Clone
    //! let copy = s.clone(); // so we can clone it
    //! ```
    //!
    //! To easily implement the Clone trait, you can also use
    //! `#[derive(Clone)]`. Example:
    //!
    //! ```
    //! #[derive(Clone)] // we add the Clone trait to Morpheus struct
    //! struct Morpheus {
    //!    blue_pill: f32,
    //!    red_pill: i64,
    //! }
    //!
    //! fn main() {
    //!    let f = Morpheus { blue_pill: 0.0, red_pill: 0 };
    //!    let copy = f.clone(); // and now we can clone it!
    //! }
    //! ```

    #![stable(feature = "rust1", since = "1.0.0")]

    use marker::Sized;

    /// A common trait for the ability to explicitly duplicate an object.
    ///
    /// Differs from `Copy` in that `Copy` is implicit and extremely inexpensive, while
    /// `Clone` is always explicit and may or may not be expensive. In order to enforce
    /// these characteristics, Rust does not allow you to reimplement `Copy`, but you
    /// may reimplement `Clone` and run arbitrary code.
    ///
    /// Since `Clone` is more general than `Copy`, you can automatically make anything
    /// `Copy` be `Clone` as well.
    ///
    /// ## Derivable
    ///
    /// This trait can be used with `#[derive]` if all fields are `Clone`. The `derive`d
    /// implementation of `clone()` calls `clone()` on each field.
    ///
    /// ## How can I implement `Clone`?
    ///
    /// Types that are `Copy` should have a trivial implementation of `Clone`. More formally:
    /// if `T: Copy`, `x: T`, and `y: &T`, then `let x = y.clone();` is equivalent to `let x = *y;`.
    /// Manual implementations should be careful to uphold this invariant; however, unsafe code
    /// must not rely on it to ensure memory safety.
    ///
    /// An example is an array holding more than 32 elements of a type that is `Clone`; the standard
    /// library only implements `Clone` up until arrays of size 32. In this case, the implementation of
    /// `Clone` cannot be `derive`d, but can be implemented as:
    ///
    /// ```
    /// #[derive(Copy)]
    /// struct Stats {
    ///    frequencies: [i32; 100],
    /// }
    ///
    /// impl Clone for Stats {
    ///     fn clone(&self) -> Stats { *self }
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait Clone : Sized {
        /// Returns a copy of the value.
        ///
        /// # Examples
        ///
        /// ```
        /// let hello = "Hello"; // &str implements Clone
        ///
        /// assert_eq!("Hello", hello.clone());
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        fn clone(&self) -> Self;

        /// Performs copy-assignment from `source`.
        ///
        /// `a.clone_from(&b)` is equivalent to `a = b.clone()` in functionality,
        /// but can be overridden to reuse the resources of `a` to avoid unnecessary
        /// allocations.
        #[inline(always)]
        #[stable(feature = "rust1", since = "1.0.0")]
        fn clone_from(&mut self, source: &Self) {
            *self = source.clone()
        }
    }

    // FIXME(aburka): this method is used solely by #[derive] to
    // assert that every component of a type implements Clone.
    //
    // This should never be called by user code.
    #[doc(hidden)]
    #[inline(always)]
    #[unstable(feature = "derive_clone_copy",
               reason = "deriving hack, should not be public",
               issue = "0")]
    pub fn assert_receiver_is_clone<T: Clone + ?Sized>(_: &T) {}

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<'a, T: ?Sized> Clone for &'a T {
        /// Returns a shallow copy of the reference.
        #[inline]
        fn clone(&self) -> &'a T { *self }
    }

    macro_rules! clone_impl {
        ($t:ty) => {
            #[stable(feature = "rust1", since = "1.0.0")]
            impl Clone for $t {
                /// Returns a deep copy of the value.
                #[inline]
                fn clone(&self) -> $t { *self }
            }
        }
    }

    clone_impl! { isize }
    clone_impl! { i8 }
    clone_impl! { i16 }
    clone_impl! { i32 }
    clone_impl! { i64 }

    clone_impl! { usize }
    clone_impl! { u8 }
    clone_impl! { u16 }
    clone_impl! { u32 }
    clone_impl! { u64 }

    clone_impl! { f32 }
    clone_impl! { f64 }

    clone_impl! { () }
    clone_impl! { bool }
    clone_impl! { char }

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result
+
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)