1.0.0[−][src]Trait core::default::Default
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 struct
s
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 derive
d, it will use the default value for each field's type.
How can I implement Default
?
Provides 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
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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impl Default for Error
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impl Default for SipHasher
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impl Default for AtomicBool
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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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impl Default for char
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impl Default for f32
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impl Default for f64
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impl Default for i8
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impl Default for i16
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impl Default for i32
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impl Default for i64
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impl Default for i128
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impl Default for isize
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impl Default for u8
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impl Default for u16
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impl Default for u32
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impl Default for u64
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impl Default for u128
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impl Default for usize
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impl<'_> Default for &'_ mut str
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impl<'_> Default for &'_ str
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impl<'_, T> Default for &'_ [T]
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impl<'_, T> Default for &'_ mut [T]
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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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fn default() -> BuildHasherDefault<H>
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impl<T> Default for Option<T>
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impl<T> Default for Empty<T>
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impl<T> Default for AtomicPtr<T>
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impl<T> Default for [T; 0]
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impl<T> Default for [T; 1] where
T: Default,
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T: Default,
impl<T> Default for [T; 2] where
T: Default,
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T: Default,
impl<T> Default for [T; 3] where
T: Default,
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T: Default,
impl<T> Default for [T; 4] where
T: Default,
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T: Default,
impl<T> Default for [T; 5] where
T: Default,
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T: Default,
impl<T> Default for [T; 6] where
T: Default,
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T: Default,
impl<T> Default for [T; 7] where
T: Default,
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T: Default,
impl<T> Default for [T; 8] where
T: Default,
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T: Default,
impl<T> Default for [T; 9] where
T: Default,
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T: Default,
impl<T> Default for [T; 10] where
T: Default,
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T: Default,
impl<T> Default for [T; 11] where
T: Default,
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T: Default,
impl<T> Default for [T; 12] where
T: Default,
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T: Default,
impl<T> Default for [T; 13] where
T: Default,
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T: Default,
impl<T> Default for [T; 14] where
T: Default,
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T: Default,
impl<T> Default for [T; 15] where
T: Default,
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T: Default,
impl<T> Default for [T; 16] where
T: Default,
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T: Default,
impl<T> Default for [T; 17] where
T: Default,
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T: Default,
impl<T> Default for [T; 18] where
T: Default,
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T: Default,
impl<T> Default for [T; 19] where
T: Default,
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T: Default,
impl<T> Default for [T; 20] where
T: Default,
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T: Default,
impl<T> Default for [T; 21] where
T: Default,
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T: Default,
impl<T> Default for [T; 22] where
T: Default,
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T: Default,
impl<T> Default for [T; 23] where
T: Default,
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T: Default,
impl<T> Default for [T; 24] where
T: Default,
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T: Default,
impl<T> Default for [T; 25] where
T: Default,
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T: Default,
impl<T> Default for [T; 26] where
T: Default,
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T: Default,
impl<T> Default for [T; 27] where
T: Default,
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T: Default,
impl<T> Default for [T; 28] where
T: Default,
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T: Default,
impl<T> Default for [T; 29] where
T: Default,
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T: Default,
impl<T> Default for [T; 30] where
T: Default,
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T: Default,
impl<T> Default for [T; 31] where
T: Default,
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T: Default,
impl<T> Default for [T; 32] where
T: Default,
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T: Default,
impl<T: Default + ?Sized> Default for ManuallyDrop<T>
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fn default() -> ManuallyDrop<T>
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impl<T: Default> Default for Cell<T>
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impl<T: Default> Default for RefCell<T>
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impl<T: Default> Default for UnsafeCell<T>
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fn default() -> UnsafeCell<T>
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Creates an UnsafeCell
, with the Default
value for T.