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    // Copyright 2012 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 `Drop` trait is used to run some code when a value goes out of scope.
    /// This is sometimes called a 'destructor'.
    ///
    /// When a value goes out of scope, if it implements this trait, it will have
    /// its `drop` method called. Then any fields the value contains will also
    /// be dropped recursively.
    ///
    /// Because of the recursive dropping, you do not need to implement this trait
    /// unless your type needs its own destructor logic.
    ///
    /// # Examples
    ///
    /// A trivial implementation of `Drop`. The `drop` method is called when `_x`
    /// goes out of scope, and therefore `main` prints `Dropping!`.
    ///
    /// ```
    /// struct HasDrop;
    ///
    /// impl Drop for HasDrop {
    ///     fn drop(&mut self) {
    ///         println!("Dropping!");
    ///     }
    /// }
    ///
    /// fn main() {
    ///     let _x = HasDrop;
    /// }
    /// ```
    ///
    /// Showing the recursive nature of `Drop`. When `outer` goes out of scope, the
    /// `drop` method will be called first for `Outer`, then for `Inner`. Therefore
    /// `main` prints `Dropping Outer!` and then `Dropping Inner!`.
    ///
    /// ```
    /// struct Inner;
    /// struct Outer(Inner);
    ///
    /// impl Drop for Inner {
    ///     fn drop(&mut self) {
    ///         println!("Dropping Inner!");
    ///     }
    /// }
    ///
    /// impl Drop for Outer {
    ///     fn drop(&mut self) {
    ///         println!("Dropping Outer!");
    ///     }
    /// }
    ///
    /// fn main() {
    ///     let _x = Outer(Inner);
    /// }
    /// ```
    ///
    /// Because variables are dropped in the reverse order they are declared,
    /// `main` will print `Declared second!` and then `Declared first!`.
    ///
    /// ```
    /// struct PrintOnDrop(&'static str);
    ///
    /// fn main() {
    ///     let _first = PrintOnDrop("Declared first!");
    ///     let _second = PrintOnDrop("Declared second!");
    /// }
    /// ```
    #[lang = "drop"]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait Drop {
        /// A method called when the value goes out of scope.
        ///
        /// When this method has been called, `self` has not yet been deallocated.
        /// If it were, `self` would be a dangling reference.
        ///
        /// After this function is over, the memory of `self` will be deallocated.
        ///
        /// This function cannot be called explicitly. This is compiler error
        /// [E0040]. However, the [`std::mem::drop`] function in the prelude can be
        /// used to call the argument's `Drop` implementation.
        ///
        /// [E0040]: ../../error-index.html#E0040
        /// [`std::mem::drop`]: ../../std/mem/fn.drop.html
        ///
        /// # Panics
        ///
        /// Given that a `panic!` will call `drop()` as it unwinds, any `panic!` in
        /// a `drop()` implementation will likely abort.
        #[stable(feature = "rust1", since = "1.0.0")]
        fn drop(&mut self);
    }

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