Module std::default
[−]
[src]
The Default
trait for types which may have meaningful default values.
Sometimes, you want to fall back to some kind of default value, and
don't particularly care what it is. This comes up often with struct
s
that define a set of options:
struct SomeOptions { foo: i32, bar: f32, }
How can we define some default values? You can use Default
:
#[derive(Default)] struct SomeOptions { foo: i32, bar: f32, } fn main() { let options: SomeOptions = Default::default(); }
Now, you get all of the default values. Rust implements Default
for various primitives types.
If you have your own type, you need to implement Default
yourself:
enum Kind { A, B, C, } impl Default for Kind { fn default() -> Kind { Kind::A } } #[derive(Default)] struct SomeOptions { foo: i32, bar: f32, baz: Kind, } fn main() { let options: SomeOptions = Default::default(); }
If you want to override a particular option, but still retain the other defaults:
fn main() { let options = SomeOptions { foo: 42, ..Default::default() }; }
Traits
Default |
A trait for giving a type a useful default value. |