Trait std::default::Default 1.0.0
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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 ReseedWithDefaultimpl<T> Default for [T; 1] where
T: Default,impl<T> Default for [T; 13] where
T: Default,impl<T> Default for [T; 12] where
T: Default,impl<A, B, C> Default for (A, B, C) where
A: Default,
B: Default,
C: Default,impl Default for boolimpl<T> Default for Option<T>impl<A, B> Default for (A, B) where
A: Default,
B: Default,impl Default for i8impl Default for f32impl<T> Default for RefCell<T> where
T: Default,impl Default for AtomicI32impl Default for AtomicU64impl<T> Default for [T; 3] where
T: Default,impl<T> Default for [T; 23] where
T: Default,impl<T> Default for [T; 14] where
T: Default,impl<A> Default for (A,) where
A: Default,impl Default for i32impl<T> Default for [T; 19] where
T: Default,impl Default for AtomicIsizeimpl<T> Default for [T; 11] where
T: Default,impl<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 AtomicBoolimpl<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 AtomicUsizeimpl<'a, T> Default for &'a mut [T]impl<T> Default for Wrapping<T> where
T: Default,impl<T> Default for UnsafeCell<T> where
T: Default,impl<T> Default for PhantomData<T> where
T: ?Sized,impl<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<T> Default for [T; 30] where
T: Default,impl Default for u16impl<T> Default for [T; 27] where
T: Default,impl<T> Default for [T; 25] where
T: Default,impl<T> Default for [T; 26] where
T: Default,impl<T> Default for [T; 5] where
T: Default,impl Default for AtomicI8impl Default for u128impl<T> Default for Empty<T>impl<T> Default for [T; 9] where
T: Default,impl<T> Default for [T; 16] where
T: Default,impl<T> Default for [T; 8] where
T: Default,impl<H> Default for BuildHasherDefault<H>impl<T> Default for Cell<T> where
T: Default,impl Default for usizeimpl<T> Default for [T; 18] 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<T> Default for [T; 24] where
T: Default,impl<T> Default for [T; 2] where
T: Default,impl Default for charimpl<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<T> Default for [T; 20] where
T: Default,impl Default for AtomicI16impl Default for f64impl<A, B, C, D> Default for (A, B, C, D) where
A: Default,
B: Default,
C: Default,
D: Default,impl<T> Default for [T; 31] where
T: Default,impl Default for u64impl Default for Errorimpl<T> Default for [T; 6] where
T: Default,impl<T> Default for [T; 29] where
T: Default,impl Default for SipHasherimpl<T> Default for [T; 32] where
T: Default,impl<T> Default for [T; 22] where
T: Default,impl<T> Default for [T; 4] where
T: Default,impl<T> Default for [T; 7] where
T: Default,impl Default for i128impl<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 Default for u8impl Default for AtomicI64impl<'a> Default for &'a strimpl<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 AtomicU32impl<T> Default for [T; 17] where
T: Default,impl<T> Default for AtomicPtr<T>impl<'a, T> Default for &'a [T]impl Default for SipHasher13impl<T> Default for [T; 0]impl<T> Default for [T; 15] where
T: Default,impl Default for ()impl<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 AtomicU8impl Default for i64impl<T> Default for [T; 10] where
T: Default,impl<T> Default for [T; 21] where
T: Default,impl Default for u32impl Default for SipHasher24impl Default for AtomicU16impl Default for i16impl<T> Default for [T; 28] where
T: Default,impl Default for isizeimpl<T> Default for Arc<T> where
T: Default,impl<T> Default for LinkedList<T>impl<T> Default for std::rc::Weak<T>impl<T> Default for Box<[T]>impl<K, V> Default for BTreeMap<K, V> where
K: Ord,impl<T> Default for BTreeSet<T> where
T: Ord,impl<T> Default for VecDeque<T>impl<T> Default for Vec<T>impl<T> Default for Rc<T> where
T: Default,impl Default for Box<str>impl Default for Stringimpl<T> Default for BinaryHeap<T> where
T: Ord,impl Default for Heapimpl<T> Default for std::sync::Weak<T>impl<T> Default for Box<T> where
T: Default,impl<'a, B> Default for Cow<'a, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,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>impl Default for Duration