Trait core::default::Default 1.0.0[−][src]
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() -> Self { Kind::A } }Run
Examples
#[derive(Default)] struct SomeOptions { foo: i32, bar: f32, }Run
Required methods
fn default() -> Self[src]
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() -> Self { Kind::A } }Run
Implementors
impl Default for PhantomPinned1.33.0[src]
impl Default for PhantomPinned1.33.0[src]fn default() -> PhantomPinned[src]
impl Default for AtomicBool[src]
impl Default for AtomicBool[src]impl Default for AtomicI128[src]
impl Default for AtomicI128[src]impl Default for AtomicIsize[src]
impl Default for AtomicIsize[src]impl Default for AtomicU128[src]
impl Default for AtomicU128[src]impl Default for AtomicUsize[src]
impl Default for AtomicUsize[src]impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default> Default for (A, B, C, D, E, F)[src]
impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default> Default for (A, B, C, D, E, F)[src]impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default> Default for (A, B, C, D, E, F, G)[src]
impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default> Default for (A, B, C, D, E, F, G)[src]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)[src]
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)[src]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)[src]
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)[src]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)[src]
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)[src]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)[src]
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)[src]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)[src]
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)[src]impl<H> Default for BuildHasherDefault<H>1.7.0[src]
impl<H> Default for BuildHasherDefault<H>1.7.0[src]fn default() -> BuildHasherDefault<H>[src]
impl<T: Default + ?Sized> Default for ManuallyDrop<T>1.20.0[src]
impl<T: Default + ?Sized> Default for ManuallyDrop<T>1.20.0[src]fn default() -> ManuallyDrop<T>[src]
impl<T: Default> Default for UnsafeCell<T>1.10.0[src]
impl<T: Default> Default for UnsafeCell<T>1.10.0[src]fn default() -> UnsafeCell<T>[src]
Creates an UnsafeCell, with the Default value for T.