core::default

Traits

Default

Trait core::default::DefaultStable [-]  [+] [src]

pub trait Default {
    fn default() -> Self;
}

A trait that types which have a useful default value should implement.

A struct can derive default implementations of Default for basic types using #[deriving(Default)].

Examples

fn main() { #[deriving(Default)] struct SomeOptions { foo: int, bar: f32, } }
#[deriving(Default)]
struct SomeOptions {
    foo: int,
    bar: f32,
}

Required Methods

fn default() -> Self

Returns the "default value" for a type.

Default values are often some kind of initial value, identity value, or anything else that may make sense as a default.

Examples

Using built-in default values:

fn main() { use std::default::Default; let i: i8 = Default::default(); let (x, y): (Option<String>, f64) = Default::default(); let (a, b, (c, d)): (int, uint, (bool, bool)) = Default::default(); }
use std::default::Default;

let i: i8 = Default::default();
let (x, y): (Option<String>, f64) = Default::default();
let (a, b, (c, d)): (int, uint, (bool, bool)) = Default::default();

Making your own:

fn main() { use std::default::Default; enum Kind { A, B, C, } impl Default for Kind { fn default() -> Kind { Kind::A } } }
use std::default::Default;

enum Kind {
    A,
    B,
    C,
}

impl Default for Kind {
    fn default() -> Kind { Kind::A }
}

Implementors