Trait std::default::Default 1.0.0[−][src]
pub trait Default {
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 Default for charimpl Default for boolimpl<T> Default for [T; 17] where
T: Default,impl<A, B, C, D, E, F, G, H> Default for (A, B, C, D, E, F, G, H) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,impl<A, B, C> Default for (A, B, C) where
A: Default,
B: Default,
C: Default,impl Default for i16x16impl<T> Default for ManuallyDrop<T> where
T: Default,impl Default for m1x64impl Default for m8x32impl Default for AtomicU16impl<'a, T> Default for &'a [T]impl Default for u16x8impl<T> Default for [T; 18] where
T: Default,impl Default for i8x64impl Default for i8x8impl<A, B, C, D, E, F, G> Default for (A, B, C, D, E, F, G) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,impl Default for m8x16impl Default for u16x32impl<T> Default for [T; 8] where
T: Default,impl<T> Default for [T; 6] where
T: Default,impl Default for m16x16impl<T> Default for [T; 0]impl<T> Default for [T; 1] where
T: Default,impl<T> Default for [T; 7] where
T: Default,impl<T> Default for [T; 28] where
T: Default,impl Default for AtomicI32impl<A, B, C, D, E, F, G, H, I, J, K, L> Default for (A, B, C, D, E, F, G, H, I, J, K, L) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: Default,
J: Default,
K: Default,
L: Default,impl<T> Default for PhantomData<T> where
T: ?Sized,impl<T> Default for [T; 22] where
T: Default,impl Default for m64x4impl<T> Default for [T; 10] where
T: Default,impl Default for SipHasherimpl Default for f32x2impl<T> Default for [T; 2] where
T: Default,impl<T> Default for [T; 9] where
T: Default,impl<T> Default for [T; 19] where
T: Default,impl<T> Default for [T; 23] where
T: Default,impl Default for u16impl Default for f32impl<A, B> Default for (A, B) where
A: Default,
B: Default,impl Default for i16x32impl<T> Default for [T; 26] where
T: Default,impl<A, B, C, D, E, F, G, H, I, J, K> Default for (A, B, C, D, E, F, G, H, I, J, K) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: Default,
J: Default,
K: Default,impl Default for i64x2impl Default for i32impl<T> Default for [T; 5] where
T: Default,impl Default for u8x64impl<T> Default for [T; 12] where
T: Default,impl Default for m8x4impl Default for i32x16impl Default for m32x4impl Default for i8x16impl<T> Default for [T; 31] where
T: Default,impl<T> Default for [T; 25] where
T: Default,impl Default for u32x4impl Default for u32x2impl Default for i64x4impl<T> Default for Reverse<T> where
T: Default,impl<T> Default for [T; 4] where
T: Default,impl<'a> Default for &'a strimpl Default for i8x32impl<A, B, C, D, E, F, G, H, I, J> Default for (A, B, C, D, E, F, G, H, I, J) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: Default,
J: Default,impl Default for m16x2impl<H> Default for BuildHasherDefault<H>impl<T> Default for [T; 11] where
T: Default,impl Default for i16impl<A, B, C, D, E, F, G, H, I> Default for (A, B, C, D, E, F, G, H, I) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: Default,impl Default for AtomicI16impl Default for f64impl Default for m16x8impl<T> Default for [T; 21] where
T: Default,impl Default for u16x4impl Default for u8x32impl Default for f32x8impl Default for m64x2impl Default for f32x16impl Default for u16x2impl<T> Default for Option<T>impl Default for f64x4impl Default for f32x4impl Default for AtomicU8impl Default for i32x2impl Default for i8x4impl Default for m32x8impl Default for AtomicIsizeimpl Default for m16x4impl<T> Default for Wrapping<T> where
T: Default,impl Default for i8x2impl Default for u128impl<A, B, C, D, E, F> Default for (A, B, C, D, E, F) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,impl Default for u8impl<T> Default for [T; 20] where
T: Default,impl Default for AtomicU32impl Default for m1x32impl Default for u64x8impl Default for AtomicBoolimpl Default for u8x8impl Default for u8x2impl Default for i64x8impl Default for m8x8impl Default for u32x16impl Default for f64x2impl<T> Default for [T; 13] where
T: Default,impl Default for u32impl Default for AtomicU64impl<T> Default for UnsafeCell<T> where
T: Default,impl<T> Default for RefCell<T> where
T: Default,impl Default for i16x8impl<A, B, C, D> Default for (A, B, C, D) where
A: Default,
B: Default,
C: Default,
D: Default,impl Default for isizeimpl<T> Default for [T; 29] where
T: Default,impl Default for m8x2impl Default for usizeimpl<T> Default for AtomicPtr<T>impl Default for u64x4impl Default for u16x16impl<T> Default for [T; 30] where
T: Default,impl Default for m32x2impl<T> Default for [T; 15] where
T: Default,impl<T> Default for [T; 27] where
T: Default,impl<T> Default for [T; 16] where
T: Default,impl<T> Default for [T; 24] where
T: Default,impl<A> Default for (A,) where
A: Default,impl Default for u8x16impl Default for AtomicUsizeimpl Default for u64impl Default for u64x2impl Default for i8impl Default for i128impl Default for Errorimpl Default for i32x8impl<T> Default for [T; 3] where
T: Default,impl<T> Default for [T; 32] where
T: Default,impl<'a, T> Default for &'a mut [T]impl Default for m1x8impl Default for f64x8impl<T> Default for Cell<T> where
T: Default,impl Default for m1x16impl Default for i32x4impl Default for i16x4impl Default for AtomicI8impl<T> Default for Empty<T>impl Default for AtomicI64impl Default for Durationimpl Default for ()impl Default for i64impl Default for i16x2impl<T> Default for [T; 14] where
T: Default,impl<A, B, C, D, E> Default for (A, B, C, D, E) where
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,impl Default for u8x4impl Default for u32x8impl<T> Default for LinkedList<T>impl<T> Default for std::rc::Weak<T>impl<T> Default for Box<T> where
T: Default,impl Default for Stringimpl<T> Default for BinaryHeap<T> where
T: Ord,impl<T> Default for Arc<T> where
T: Default,impl<T> Default for std::sync::Weak<T>impl<T> Default for VecDeque<T>impl Default for Box<str>impl<T> Default for Rc<T> where
T: Default,impl<T> Default for Box<[T]>impl Default for Globalimpl<K, V> Default for BTreeMap<K, V> where
K: Ord,impl<T> Default for BTreeSet<T> where
T: Ord,impl<'a, B> Default for Cow<'a, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,impl<T> Default for Vec<T>impl<K, V, S> Default for HashMap<K, V, S> where
K: Eq + Hash,
S: BuildHasher + Default,impl Default for DefaultHasherimpl Default for RandomStateimpl<T, S> Default for HashSet<T, S> where
T: Eq + Hash,
S: BuildHasher + Default,impl<'a> Default for &'a CStrimpl Default for CStringimpl Default for Box<CStr>impl Default for OsStringimpl Default for Box<OsStr>impl<'a> Default for &'a OsStrimpl Default for PathBufimpl Default for Condvarimpl<T: ?Sized + Default> Default for Mutex<T>impl<T: Default> Default for RwLock<T>