1.0.0[−][src]Trait std::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 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?
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
Implementations on Foreign Types
impl<K, V, S> Default for HashMap<K, V, S> where
S: BuildHasher + Default,
S: BuildHasher + Default,
fn default() -> HashMap<K, V, S>
Creates an empty HashMap<K, V, S>, with the Default value for the hasher.
impl<T, S> Default for HashSet<T, S> where
S: BuildHasher + Default,
T: Eq + Hash,
S: BuildHasher + Default,
T: Eq + Hash,
fn default() -> HashSet<T, S>
Creates an empty HashSet<T, S> with the Default value for the hasher.
Implementors
impl Default for bool[src]
impl Default for char[src]
impl Default for f32[src]
impl Default for f64[src]
impl Default for i128[src]
impl Default for i16[src]
impl Default for i32[src]
impl Default for i64[src]
impl Default for i8[src]
impl Default for isize[src]
impl Default for u128[src]
impl Default for u16[src]
impl Default for u32[src]
impl Default for u64[src]
impl Default for u8[src]
impl Default for ()[src]
impl Default for usize[src]
impl Default for Global[src]
impl Default for System[src]
impl Default for Box<str>[src]
impl Default for Box<CStr>[src]
impl Default for Box<OsStr>[src]
impl Default for DefaultHasher[src]
fn default() -> DefaultHasher[src]
Creates a new DefaultHasher using new.
See its documentation for more.
impl Default for RandomState[src]
fn default() -> RandomState[src]
Constructs a new RandomState.
impl Default for CString[src]
impl Default for OsString[src]
impl Default for Error[src]
impl Default for SipHasher[src]
impl Default for PathBuf[src]
impl Default for String[src]
impl Default for AtomicBool[src]
fn default() -> AtomicBool[src]
Creates an AtomicBool initialized to false.
impl Default for AtomicI128[src]
fn default() -> AtomicI128[src]
impl Default for AtomicI16[src]
impl Default for AtomicI32[src]
impl Default for AtomicI64[src]
impl Default for AtomicI8[src]
impl Default for AtomicIsize[src]
fn default() -> AtomicIsize[src]
impl Default for AtomicU128[src]
fn default() -> AtomicU128[src]
impl Default for AtomicU16[src]
impl Default for AtomicU32[src]
impl Default for AtomicU64[src]
impl Default for AtomicU8[src]
impl Default for AtomicUsize[src]
fn default() -> AtomicUsize[src]
impl Default for Condvar[src]
impl Default for Duration[src]
impl<'_> Default for &'_ str[src]
impl<'_> Default for &'_ CStr[src]
impl<'_> Default for &'_ OsStr[src]
impl<'_> Default for &'_ mut str[src]
impl<'_, B> Default for Cow<'_, B> where
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default, [src]
B: ToOwned + ?Sized,
<B as ToOwned>::Owned: Default,
fn default() -> Cow<'_, B>[src]
Creates an owned Cow<'a, B> with the default value for the contained owned value.
impl<'_, T> Default for &'_ [T][src]
impl<'_, T> Default for &'_ mut [T][src]
impl<A> Default for (A,) where
A: Default, [src]
A: Default,
impl<A, B> Default for (A, B) where
A: Default,
B: Default, [src]
A: Default,
B: Default,
impl<A, B, C> Default for (A, B, C) where
A: Default,
B: Default,
C: Default, [src]
A: Default,
B: Default,
C: Default,
impl<A, B, C, D> Default for (A, B, C, D) where
A: Default,
B: Default,
C: Default,
D: Default, [src]
A: Default,
B: Default,
C: Default,
D: 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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
impl<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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: 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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: 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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: Default,
J: 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, [src]
A: Default,
B: Default,
C: Default,
D: Default,
E: Default,
F: Default,
G: Default,
H: Default,
I: Default,
J: Default,
K: Default,
impl<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, [src]
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<H> Default for BuildHasherDefault<H>[src]
fn default() -> BuildHasherDefault<H>[src]
impl<K, V> Default for BTreeMap<K, V> where
K: Ord, [src]
K: Ord,
impl<K, V, S> Default for std::collections::HashMap<K, V, S> where
K: Eq + Hash,
S: BuildHasher + Default, [src]
K: Eq + Hash,
S: BuildHasher + Default,
fn default() -> HashMap<K, V, S>[src]
Creates an empty HashMap<K, V, S>, with the Default value for the hasher.
impl<T> Default for Option<T>[src]
impl<T> Default for [T; 0][src]
impl<T> Default for [T; 1] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 2] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 3] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 4] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 5] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 6] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 7] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 8] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 9] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 10] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 11] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 12] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 13] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 14] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 15] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 16] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 17] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 18] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 19] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 20] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 21] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 22] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 23] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 24] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 25] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 26] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 27] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 28] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 29] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 30] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 31] where
T: Default, [src]
T: Default,
impl<T> Default for [T; 32] where
T: Default, [src]
T: Default,
impl<T> Default for Box<[T]>[src]
impl<T> Default for Box<T> where
T: Default, [src]
T: Default,
ⓘImportant traits for Box<I>fn default() -> Box<T>[src]
Creates a Box<T>, with the Default value for T.
impl<T> Default for Cell<T> where
T: Default, [src]
T: Default,
impl<T> Default for RefCell<T> where
T: Default, [src]
T: Default,
impl<T> Default for UnsafeCell<T> where
T: Default, [src]
T: Default,
fn default() -> UnsafeCell<T>[src]
Creates an UnsafeCell, with the Default value for T.
impl<T> Default for Reverse<T> where
T: Default, [src]
T: Default,
impl<T> Default for BinaryHeap<T> where
T: Ord, [src]
T: Ord,
fn default() -> BinaryHeap<T>[src]
Creates an empty BinaryHeap<T>.
impl<T> Default for BTreeSet<T> where
T: Ord, [src]
T: Ord,
impl<T> Default for LinkedList<T>[src]
fn default() -> LinkedList<T>[src]
Creates an empty LinkedList<T>.
impl<T> Default for VecDeque<T>[src]
impl<T> Default for Empty<T>[src]
impl<T> Default for PhantomData<T> where
T: ?Sized, [src]
T: ?Sized,
fn default() -> PhantomData<T>[src]
impl<T> Default for ManuallyDrop<T> where
T: Default + ?Sized, [src]
T: Default + ?Sized,
fn default() -> ManuallyDrop<T>[src]
impl<T> Default for Wrapping<T> where
T: Default, [src]
T: Default,
impl<T> Default for Rc<T> where
T: Default, [src]
T: Default,
impl<T> Default for std::rc::Weak<T>[src]
impl<T> Default for AtomicPtr<T>[src]
impl<T> Default for Arc<T> where
T: Default, [src]
T: Default,
impl<T> Default for std::sync::Weak<T>[src]
impl<T> Default for Vec<T>[src]
impl<T, S> Default for std::collections::HashSet<T, S> where
T: Eq + Hash,
S: BuildHasher + Default, [src]
T: Eq + Hash,
S: BuildHasher + Default,
fn default() -> HashSet<T, S>[src]
Creates an empty HashSet<T, S> with the Default value for the hasher.