1.0.0[][src]Trait core::default::Default

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() -> Self { Kind::A }
}Run

Examples

#[derive(Default)]
struct SomeOptions {
    foo: i32,
    bar: f32,
}Run

Required Methods

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 ()
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Returns the default value of ()

impl Default for Error
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impl Default for SipHasher
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impl Default for AtomicBool
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Creates an AtomicBool initialized to false.

impl Default for AtomicI16
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impl Default for AtomicI32
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impl Default for AtomicI64
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impl Default for AtomicI8
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impl Default for AtomicIsize
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impl Default for AtomicU16
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impl Default for AtomicU32
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impl Default for AtomicU64
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impl Default for AtomicU8
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impl Default for AtomicUsize
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impl Default for Duration
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impl Default for bool
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Returns the default value of false

impl Default for char
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Returns the default value of \x00

impl Default for f32
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Returns the default value of 0.0

impl Default for f64
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Returns the default value of 0.0

impl Default for i8
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Returns the default value of 0

impl Default for i16
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Returns the default value of 0

impl Default for i32
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Returns the default value of 0

impl Default for i64
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Returns the default value of 0

impl Default for i128
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Returns the default value of 0

impl Default for isize
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Returns the default value of 0

impl Default for u8
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Returns the default value of 0

impl Default for u16
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Returns the default value of 0

impl Default for u32
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Returns the default value of 0

impl Default for u64
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Returns the default value of 0

impl Default for u128
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Returns the default value of 0

impl Default for usize
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Returns the default value of 0

impl<'_> Default for &'_ mut str
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Creates an empty mutable str

impl<'_> Default for &'_ str
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Creates an empty str

impl<A: Default> Default for (A,)
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impl<A: Default, B: Default> Default for (A, B)
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impl<A: Default, B: Default, C: Default> Default for (A, B, C)
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impl<A: Default, B: Default, C: Default, D: Default> Default for (A, B, C, D)
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impl<A: Default, B: Default, C: Default, D: Default, E: Default> Default for (A, B, C, D, E)
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impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default> Default for (A, B, C, D, E, F)
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impl<A: Default, B: Default, C: Default, D: Default, E: Default, F: Default, G: Default> Default for (A, B, C, D, E, F, G)
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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)
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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)
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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)
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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)
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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)
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impl<H> Default for BuildHasherDefault<H>
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impl<T> Default for Option<T>
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Returns None.

impl<T> Default for Empty<T>
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impl<T> Default for AtomicPtr<T>
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Creates a null AtomicPtr<T>.

impl<T> Default for [T; 0]
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impl<T> Default for [T; 1] where
    T: Default
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impl<T> Default for [T; 2] where
    T: Default
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impl<T> Default for [T; 3] where
    T: Default
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impl<T> Default for [T; 4] where
    T: Default
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impl<T> Default for [T; 5] where
    T: Default
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impl<T> Default for [T; 6] where
    T: Default
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impl<T> Default for [T; 7] where
    T: Default
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impl<T> Default for [T; 8] where
    T: Default
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impl<T> Default for [T; 9] where
    T: Default
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impl<T> Default for [T; 10] where
    T: Default
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impl<T> Default for [T; 11] where
    T: Default
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impl<T> Default for [T; 12] where
    T: Default
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impl<T> Default for [T; 13] where
    T: Default
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impl<T> Default for [T; 14] where
    T: Default
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impl<T> Default for [T; 15] where
    T: Default
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impl<T> Default for [T; 16] where
    T: Default
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impl<T> Default for [T; 17] where
    T: Default
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impl<T> Default for [T; 18] where
    T: Default
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impl<T> Default for [T; 19] where
    T: Default
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impl<T> Default for [T; 20] where
    T: Default
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impl<T> Default for [T; 21] where
    T: Default
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impl<T> Default for [T; 22] where
    T: Default
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impl<T> Default for [T; 23] where
    T: Default
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impl<T> Default for [T; 24] where
    T: Default
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impl<T> Default for [T; 25] where
    T: Default
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impl<T> Default for [T; 26] where
    T: Default
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impl<T> Default for [T; 27] where
    T: Default
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impl<T> Default for [T; 28] where
    T: Default
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impl<T> Default for [T; 29] where
    T: Default
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impl<T> Default for [T; 30] where
    T: Default
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impl<T> Default for [T; 31] where
    T: Default
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impl<T> Default for [T; 32] where
    T: Default
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impl<T, '_> Default for &'_ [T]
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Creates an empty slice.

impl<T, '_> Default for &'_ mut [T]
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Creates a mutable empty slice.

impl<T: Default + ?Sized> Default for ManuallyDrop<T>
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impl<T: Default> Default for Cell<T>
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Creates a Cell<T>, with the Default value for T.

impl<T: Default> Default for RefCell<T>
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Creates a RefCell<T>, with the Default value for T.

impl<T: Default> Default for UnsafeCell<T>
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Creates an UnsafeCell, with the Default value for T.

impl<T: Default> Default for Reverse<T>
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impl<T: Default> Default for Wrapping<T>
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impl<T: ?Sized> Default for PhantomData<T>
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