mod.rs.html -- source
Description: Source to the Rust file `libcore/ops/mod.rs`.
Keywords: rust, rustlang, rust-lang

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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.

    //! Overloadable operators.
    //!
    //! Implementing these traits allows you to overload certain operators.
    //!
    //! Some of these traits are imported by the prelude, so they are available in
    //! every Rust program. Only operators backed by traits can be overloaded. For
    //! example, the addition operator (`+`) can be overloaded through the [`Add`]
    //! trait, but since the assignment operator (`=`) has no backing trait, there
    //! is no way of overloading its semantics. Additionally, this module does not
    //! provide any mechanism to create new operators. If traitless overloading or
    //! custom operators are required, you should look toward macros or compiler
    //! plugins to extend Rust's syntax.
    //!
    //! Implementations of operator traits should be unsurprising in their
    //! respective contexts, keeping in mind their usual meanings and
    //! [operator precedence]. For example, when implementing [`Mul`], the operation
    //! should have some resemblance to multiplication (and share expected
    //! properties like associativity).
    //!
    //! Note that the `&&` and `||` operators short-circuit, i.e. they only
    //! evaluate their second operand if it contributes to the result. Since this
    //! behavior is not enforceable by traits, `&&` and `||` are not supported as
    //! overloadable operators.
    //!
    //! Many of the operators take their operands by value. In non-generic
    //! contexts involving built-in types, this is usually not a problem.
    //! However, using these operators in generic code, requires some
    //! attention if values have to be reused as opposed to letting the operators
    //! consume them. One option is to occasionally use [`clone`].
    //! Another option is to rely on the types involved providing additional
    //! operator implementations for references. For example, for a user-defined
    //! type `T` which is supposed to support addition, it is probably a good
    //! idea to have both `T` and `&T` implement the traits [`Add<T>`][`Add`] and
    //! [`Add<&T>`][`Add`] so that generic code can be written without unnecessary
    //! cloning.
    //!
    //! # Examples
    //!
    //! This example creates a `Point` struct that implements [`Add`] and [`Sub`],
    //! and then demonstrates adding and subtracting two `Point`s.
    //!
    //! ```rust
    //! use std::ops::{Add, Sub};
    //!
    //! #[derive(Debug, PartialEq)]
    //! struct Point {
    //!     x: i32,
    //!     y: i32,
    //! }
    //!
    //! impl Add for Point {
    //!     type Output = Point;
    //!
    //!     fn add(self, other: Point) -> Point {
    //!         Point {x: self.x + other.x, y: self.y + other.y}
    //!     }
    //! }
    //!
    //! impl Sub for Point {
    //!     type Output = Point;
    //!
    //!     fn sub(self, other: Point) -> Point {
    //!         Point {x: self.x - other.x, y: self.y - other.y}
    //!     }
    //! }
    //!
    //! assert_eq!(Point {x: 3, y: 3}, Point {x: 1, y: 0} + Point {x: 2, y: 3});
    //! assert_eq!(Point {x: -1, y: -3}, Point {x: 1, y: 0} - Point {x: 2, y: 3});
    //! ```
    //!
    //! See the documentation for each trait for an example implementation.
    //!
    //! The [`Fn`], [`FnMut`], and [`FnOnce`] traits are implemented by types that can be
    //! invoked like functions. Note that [`Fn`] takes `&self`, [`FnMut`] takes `&mut
    //! self` and [`FnOnce`] takes `self`. These correspond to the three kinds of
    //! methods that can be invoked on an instance: call-by-reference,
    //! call-by-mutable-reference, and call-by-value. The most common use of these
    //! traits is to act as bounds to higher-level functions that take functions or
    //! closures as arguments.
    //!
    //! Taking a [`Fn`] as a parameter:
    //!
    //! ```rust
    //! fn call_with_one<F>(func: F) -> usize
    //!     where F: Fn(usize) -> usize
    //! {
    //!     func(1)
    //! }
    //!
    //! let double = |x| x * 2;
    //! assert_eq!(call_with_one(double), 2);
    //! ```
    //!
    //! Taking a [`FnMut`] as a parameter:
    //!
    //! ```rust
    //! fn do_twice<F>(mut func: F)
    //!     where F: FnMut()
    //! {
    //!     func();
    //!     func();
    //! }
    //!
    //! let mut x: usize = 1;
    //! {
    //!     let add_two_to_x = || x += 2;
    //!     do_twice(add_two_to_x);
    //! }
    //!
    //! assert_eq!(x, 5);
    //! ```
    //!
    //! Taking a [`FnOnce`] as a parameter:
    //!
    //! ```rust
    //! fn consume_with_relish<F>(func: F)
    //!     where F: FnOnce() -> String
    //! {
    //!     // `func` consumes its captured variables, so it cannot be run more
    //!     // than once
    //!     println!("Consumed: {}", func());
    //!
    //!     println!("Delicious!");
    //!
    //!     // Attempting to invoke `func()` again will throw a `use of moved
    //!     // value` error for `func`
    //! }
    //!
    //! let x = String::from("x");
    //! let consume_and_return_x = move || x;
    //! consume_with_relish(consume_and_return_x);
    //!
    //! // `consume_and_return_x` can no longer be invoked at this point
    //! ```
    //!
    //! [`Fn`]: trait.Fn.html
    //! [`FnMut`]: trait.FnMut.html
    //! [`FnOnce`]: trait.FnOnce.html
    //! [`Add`]: trait.Add.html
    //! [`Sub`]: trait.Sub.html
    //! [`Mul`]: trait.Mul.html
    //! [`clone`]: ../clone/trait.Clone.html#tymethod.clone
    //! [operator precedence]: ../../reference/expressions.html#expression-precedence

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

    mod arith;
    mod bit;
    mod deref;
    mod drop;
    mod function;
    mod generator;
    mod index;
    mod range;
    mod try;
    mod unsize;

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::arith::{Add, Sub, Mul, Div, Rem, Neg};
    #[stable(feature = "op_assign_traits", since = "1.8.0")]
    pub use self::arith::{AddAssign, SubAssign, MulAssign, DivAssign, RemAssign};

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::bit::{Not, BitAnd, BitOr, BitXor, Shl, Shr};
    #[stable(feature = "op_assign_traits", since = "1.8.0")]
    pub use self::bit::{BitAndAssign, BitOrAssign, BitXorAssign, ShlAssign, ShrAssign};

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::deref::{Deref, DerefMut};

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::drop::Drop;

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::function::{Fn, FnMut, FnOnce};

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::index::{Index, IndexMut};

    #[stable(feature = "rust1", since = "1.0.0")]
    pub use self::range::{Range, RangeFrom, RangeFull, RangeTo};

    #[stable(feature = "inclusive_range", since = "1.26.0")]
    pub use self::range::{RangeInclusive, RangeToInclusive, RangeBounds, Bound};

    #[unstable(feature = "try_trait", issue = "42327")]
    pub use self::try::Try;

    #[unstable(feature = "generator_trait", issue = "43122")]
    pub use self::generator::{Generator, GeneratorState};

    #[unstable(feature = "coerce_unsized", issue = "27732")]
    pub use self::unsize::CoerceUnsized;

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