Trait core::default::Default 1.0.0
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pub trait Default: Sized {
fn default() -> Self;
}A trait for giving a type a useful default value.
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 structs
that define a set of options:
struct SomeOptions { foo: i32, bar: f32, }Run
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(); }Run
Now, you get all of the default values. Rust implements Default for various primitives types.
If you want to override a particular option, but still retain the other defaults:
fn main() { let options = SomeOptions { foo: 42, ..Default::default() }; }Run
Derivable
This trait can be used with #[derive] if all of the type's fields implement
Default. When derived, it will use the default value for each field's type.
How can I implement Default?
Provide an implementation for the default() method that returns the value of
your type that should be the default:
enum Kind { A, B, C, } impl Default for Kind { fn default() -> Kind { Kind::A } }Run
Examples
#[derive(Default)] struct SomeOptions { foo: i32, bar: f32, }Run
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:
let i: i8 = Default::default(); let (x, y): (Option<String>, f64) = Default::default(); let (a, b, (c, d)): (i32, u32, (bool, bool)) = Default::default();Run
Making your own:
enum Kind { A, B, C, } impl Default for Kind { fn default() -> Kind { Kind::A } }Run
Implementors
impl<T: Default> Default for Wrapping<T>impl<T: Default> Default for ManuallyDrop<T>impl<T: ?Sized> Default for PhantomData<T>impl Default for ()impl Default for boolimpl Default for charimpl Default for usizeimpl Default for u8impl Default for u16impl Default for u32impl Default for u64impl Default for u128impl Default for isizeimpl Default for i8impl Default for i16impl Default for i32impl Default for i64impl Default for i128impl Default for f32impl Default for f64impl<T> Default for [T; 32] where
T: Default,impl<T> Default for [T; 31] where
T: Default,impl<T> Default for [T; 30] where
T: Default,impl<T> Default for [T; 29] where
T: Default,impl<T> Default for [T; 28] where
T: Default,impl<T> Default for [T; 27] where
T: Default,impl<T> Default for [T; 26] where
T: Default,impl<T> Default for [T; 25] where
T: Default,impl<T> Default for [T; 24] where
T: Default,impl<T> Default for [T; 23] where
T: Default,impl<T> Default for [T; 22] where
T: Default,impl<T> Default for [T; 21] where
T: Default,impl<T> Default for [T; 20] where
T: Default,impl<T> Default for [T; 19] where
T: Default,impl<T> Default for [T; 18] where
T: Default,impl<T> Default for [T; 17] where
T: Default,impl<T> Default for [T; 16] where
T: Default,impl<T> Default for [T; 15] where
T: Default,impl<T> Default for [T; 14] where
T: Default,impl<T> Default for [T; 13] where
T: Default,impl<T> Default for [T; 12] where
T: Default,impl<T> Default for [T; 11] where
T: Default,impl<T> Default for [T; 10] where
T: Default,impl<T> Default for [T; 9] where
T: Default,impl<T> Default for [T; 8] where
T: Default,impl<T> Default for [T; 7] where
T: Default,impl<T> Default for [T; 6] where
T: Default,impl<T> Default for [T; 5] where
T: Default,impl<T> Default for [T; 4] where
T: Default,impl<T> Default for [T; 3] where
T: Default,impl<T> Default for [T; 2] where
T: Default,impl<T> Default for [T; 1] where
T: Default,impl<T> Default for [T; 0]impl Default for AtomicBoolimpl<T> Default for AtomicPtr<T>impl Default for AtomicI8impl Default for AtomicU8impl Default for AtomicI16impl Default for AtomicU16impl Default for AtomicI32impl Default for AtomicU32impl Default for AtomicI64impl Default for AtomicU64impl Default for AtomicIsizeimpl Default for AtomicUsizeimpl<T: Default> Default for Cell<T>impl<T: Default> Default for RefCell<T>impl<T: Default> Default for UnsafeCell<T>impl<T> Default for Empty<T>impl<T> Default for Option<T>impl<'a, T> Default for &'a [T]impl<'a, T> Default for &'a mut [T]impl<'a> Default for &'a strimpl Default for SipHasher13impl Default for SipHasher24impl Default for SipHasherimpl<H> Default for BuildHasherDefault<H>impl Default for Errorimpl<A: Default> Default for (A,)impl<A: Default, B: Default> Default for (A, B)impl<A: Default, B: Default, C: Default> Default for (A, B, C)impl<A: Default, B: Default, C: Default, D: Default> Default for (A, B, C, D)impl<A: Default, B: Default, C: Default, D: Default, E: Default> Default for (A, B, C, D, E)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default> Default for (A, B, C, D, E, F)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default> Default for (A, B, C, D, E, F, G)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default, H: Default> Default for (A, B, C, D, E, F, G, H)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default, H: Default, I: Default> Default for (A, B, C, D, E, F, G, H, I)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default, H: Default, I: Default, J: Default> Default for (A, B, C, D, E, F, G, H, I, J)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default, H: Default, I: Default, J: Default, K: Default> Default for (A, B, C, D, E, F, G, H, I, J, K)impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default, H: Default, I: Default, J: Default, K: Default, L: Default> Default for (A, B, C, D, E, F, G, H, I, J, K, L)