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    // 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`][clone] method.
    //!
    //! [`Clone`]: trait.Clone.html
    //! [clone]: trait.Clone.html#tymethod.clone
    //! [`Drop`]: ../../std/ops/trait.Drop.html
    //!
    //! 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")]

    /// 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:
    ///
    /// [`Copy`]: ../../std/marker/trait.Copy.html
    /// [`clone`]: trait.Clone.html#tymethod.clone
    ///
    /// ```
    /// #[derive(Copy)]
    /// struct Stats {
    ///    frequencies: [i32; 100],
    /// }
    ///
    /// impl Clone for Stats {
    ///     fn clone(&self) -> Stats { *self }
    /// }
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[lang = "clone"]
    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]
        #[stable(feature = "rust1", since = "1.0.0")]
        fn clone_from(&mut self, source: &Self) {
            *self = source.clone()
        }
    }

    // FIXME(aburka): these structs are used solely by #[derive] to
    // assert that every component of a type implements Clone or Copy.
    //
    // These structs should never appear in user code.
    #[doc(hidden)]
    #[allow(missing_debug_implementations)]
    #[unstable(feature = "derive_clone_copy",
               reason = "deriving hack, should not be public",
               issue = "0")]
    pub struct AssertParamIsClone<T: Clone + ?Sized> { _field: ::marker::PhantomData<T> }
    #[doc(hidden)]
    #[allow(missing_debug_implementations)]
    #[unstable(feature = "derive_clone_copy",
               reason = "deriving hack, should not be public",
               issue = "0")]
    pub struct AssertParamIsCopy<T: Copy + ?Sized> { _field: ::marker::PhantomData<T> }

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