1.0.0[−][src]Trait sp_std::default::Default

pub trait Default {
    pub 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,
}

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();
}

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() };
}

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 }
}

Examples

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

Required methods

pub fn default() -> Self[src]

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();

Making your own:

enum Kind {
    A,
    B,
    C,
}

impl Default for Kind {
    fn default() -> Self { Kind::A }
}
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Implementations on Foreign Types

impl<T, S> Default for HashSet<T, S> where
    S: Default, [src]

pub fn default() -> HashSet<T, S>[src]

Creates an empty HashSet<T, S> with the Default value for the hasher.

impl<T> Default for Cursor<T> where
    T: Default, [src]

impl<T> Default for SyncOnceCell<T>[src]

impl Default for DefaultHasher[src]

pub fn default() -> DefaultHasher[src]

Creates a new DefaultHasher using new. See its documentation for more.

impl<'_> Default for &'_ CStr[src]

impl Default for CString[src]

pub fn default() -> CString[src]

Creates an empty CString.

impl<'_> Default for &'_ OsStr[src]

pub fn default() -> &'_ OsStr[src]

Creates an empty OsStr.

impl Default for PathBuf[src]

impl Default for OsString[src]

pub fn default() -> OsString[src]

Constructs an empty OsString.

impl<T> Default for SyncLazy<T, fn() -> T> where
    T: Default, [src]

pub fn default() -> SyncLazy<T, fn() -> T>[src]

Creates a new lazy value using Default as the initializing function.

impl<K, V, S> Default for HashMap<K, V, S> where
    S: Default, [src]

pub fn default() -> HashMap<K, V, S>[src]

Creates an empty HashMap<K, V, S>, with the Default value for the hasher.

impl Default for RandomState[src]

pub fn default() -> RandomState[src]

Constructs a new RandomState.

impl<T> Default for [T; 20] where
    T: Default, [src]

impl<T> Default for [T; 7] where
    T: Default, [src]

impl Default for u64[src]

pub fn default() -> u64[src]

Returns the default value of 0

impl<T> Default for [T; 23] where
    T: Default, [src]

impl<T> Default for [T; 0][src]

impl Default for isize[src]

pub fn default() -> isize[src]

Returns the default value of 0

impl<T> Default for [T; 12] where
    T: Default, [src]

impl<T> Default for OnceCell<T>[src]

impl Default for i32[src]

pub fn default() -> i32[src]

Returns the default value of 0

impl<A, B, C> Default for (A, B, C) where
    C: Default,
    A: Default,
    B: Default, [src]

impl<T> Default for [T; 19] where
    T: Default, [src]

impl<T> Default for [T; 30] where
    T: Default, [src]

impl<T> Default for [T; 9] where
    T: Default, [src]

impl<A, B, C, D, E> Default for (A, B, C, D, E) where
    C: Default,
    A: Default,
    E: Default,
    B: Default,
    D: Default, [src]

impl Default for u128[src]

pub fn default() -> u128[src]

Returns the default value of 0

impl<T> Default for [T; 6] where
    T: Default, [src]

impl Default for f64[src]

pub fn default() -> f64[src]

Returns the default value of 0.0

impl Default for Duration[src]

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
    C: Default,
    A: Default,
    E: Default,
    K: Default,
    F: Default,
    I: Default,
    B: Default,
    H: Default,
    D: Default,
    G: Default,
    J: Default, [src]

impl Default for bool[src]

pub fn default() -> bool[src]

Returns the default value of false

impl<T> Default for [T; 11] where
    T: Default, [src]

impl Default for i16[src]

pub fn default() -> i16[src]

Returns the default value of 0

impl Default for ()[src]

pub fn default()[src]

Returns the default value of ()

impl<T> Default for [T; 31] where
    T: Default, [src]

impl<T> Default for [T; 24] where
    T: Default, [src]

impl<T> Default for [T; 25] where
    T: Default, [src]

impl<T> Default for [T; 4] where
    T: Default, [src]

impl<T> Default for [T; 22] where
    T: Default, [src]

impl Default for i64[src]

pub fn default() -> i64[src]

Returns the default value of 0

impl<T> Default for [T; 14] where
    T: Default, [src]

impl<T> Default for [T; 8] where
    T: Default, [src]

impl Default for u32[src]

pub fn default() -> u32[src]

Returns the default value of 0

impl<T> Default for [T; 1] where
    T: Default, [src]

impl Default for i8[src]

pub fn default() -> i8[src]

Returns the default value of 0

impl<T> Default for [T; 26] where
    T: Default, [src]

impl<A, B, C, D, E, F> Default for (A, B, C, D, E, F) where
    C: Default,
    A: Default,
    E: Default,
    F: Default,
    B: Default,
    D: Default, [src]

impl<'_> Default for &'_ mut str[src]

pub fn default() -> &'_ mut str[src]

Creates an empty mutable str

impl<A, B, C, D, E, F, G, H, I> Default for (A, B, C, D, E, F, G, H, I) where
    C: Default,
    A: Default,
    E: Default,
    F: Default,
    I: Default,
    B: Default,
    H: Default,
    D: Default,
    G: Default, [src]

impl<T> Default for [T; 5] where
    T: Default, [src]

impl<A, B, C, D> Default for (A, B, C, D) where
    C: Default,
    A: Default,
    B: Default,
    D: Default, [src]

impl<'_> Default for &'_ str[src]

pub fn default() -> &'_ str[src]

Creates an empty str

impl<T> Default for [T; 15] where
    T: Default, [src]

impl<T> Default for [T; 2] where
    T: Default, [src]

impl<A, B, C, D, E, F, G, H, I, J> Default for (A, B, C, D, E, F, G, H, I, J) where
    C: Default,
    A: Default,
    E: Default,
    F: Default,
    I: Default,
    B: Default,
    H: Default,
    D: Default,
    G: Default,
    J: Default, [src]

impl<T> Default for [T; 17] where
    T: Default, [src]

impl Default for i128[src]

pub fn default() -> i128[src]

Returns the default value of 0

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
    C: Default,
    A: Default,
    E: Default,
    K: Default,
    F: Default,
    I: Default,
    B: Default,
    H: Default,
    D: Default,
    G: Default,
    J: Default,
    L: Default, [src]

impl<T> Default for Lazy<T, fn() -> T> where
    T: Default, [src]

pub fn default() -> Lazy<T, fn() -> T>[src]

Creates a new lazy value using Default as the initializing function.

impl Default for u16[src]

pub fn default() -> u16[src]

Returns the default value of 0

impl<A, B> Default for (A, B) where
    A: Default,
    B: Default, [src]

impl Default for u8[src]

pub fn default() -> u8[src]

Returns the default value of 0

impl<T> Default for [T; 18] where
    T: Default, [src]

impl<A> Default for (A,) where
    A: Default, [src]

impl<T> Default for Option<T>[src]

pub fn default() -> Option<T>[src]

Returns None.

Examples

let opt: Option<u32> = Option::default();
assert!(opt.is_none());

impl Default for usize[src]

pub fn default() -> usize[src]

Returns the default value of 0

impl Default for f32[src]

pub fn default() -> f32[src]

Returns the default value of 0.0

impl<T> Default for [T; 3] where
    T: Default, [src]

impl<'_, T> Default for &'_ mut [T][src]

pub fn default() -> &'_ mut [T]ⓘ

Notable traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
[src]

Creates a mutable empty slice.

impl<T> Default for [T; 29] where
    T: Default, [src]

impl<'_, T> Default for &'_ [T][src]

pub fn default() -> &'_ [T]ⓘ

Notable traits for &'_ [u8]

impl<'_> Read for &'_ [u8]impl<'_> Write for &'_ mut [u8]
[src]

Creates an empty slice.

impl<T> Default for [T; 13] where
    T: Default, [src]

impl<A, B, C, D, E, F, G> Default for (A, B, C, D, E, F, G) where
    C: Default,
    A: Default,
    E: Default,
    F: Default,
    B: Default,
    D: Default,
    G: Default, [src]

impl<T> Default for [T; 10] where
    T: Default, [src]

impl<T> Default for [T; 27] where
    T: Default, [src]

impl Default for char[src]

pub fn default() -> char[src]

Returns the default value of \x00

impl<T> Default for [T; 21] where
    T: Default, [src]

impl<T> Default for [T; 28] where
    T: Default, [src]

impl<T> Default for [T; 32] where
    T: Default, [src]

impl<T> Default for [T; 16] where
    T: Default, [src]

impl<A, B, C, D, E, F, G, H> Default for (A, B, C, D, E, F, G, H) where
    C: Default,
    A: Default,
    E: Default,
    F: Default,
    B: Default,
    H: Default,
    D: Default,
    G: Default, [src]

impl Default for String[src]

pub fn default() -> String[src]

Creates an empty String.

impl<T> Default for BinaryHeap<T> where
    T: Ord, [src]

pub fn default() -> BinaryHeap<T>[src]

Creates an empty BinaryHeap<T>.

impl<T> Default for LinkedList<T>[src]

pub fn default() -> LinkedList<T>[src]

Creates an empty LinkedList<T>.

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Implementors

impl Default for Global[src]

impl Default for System[src]

impl Default for Error[src]

impl Default for SipHasher[src]

impl Default for PhantomPinned[src]

impl Default for RangeFull[src]

impl Default for Box<str, Global>[src]

impl Default for Box<CStr, Global>[src]

impl Default for Box<OsStr, Global>[src]

impl Default for Writer[src]

impl Default for AtomicBool[src]

pub fn default() -> AtomicBool[src]

Creates an AtomicBool initialized to false.

impl Default for AtomicI8[src]

impl Default for AtomicI16[src]

impl Default for AtomicI32[src]

impl Default for AtomicI64[src]

impl Default for AtomicIsize[src]

impl Default for AtomicU8[src]

impl Default for AtomicU16[src]

impl Default for AtomicU32[src]

impl Default for AtomicU64[src]

impl Default for AtomicUsize[src]

impl Default for Condvar[src]

pub fn default() -> Condvar[src]

Creates a Condvar which is ready to be waited on and notified.

impl<'_, B> Default for Cow<'_, B> where
    B: ToOwned + ?Sized,
    <B as ToOwned>::Owned: Default, [src]

pub fn default() -> Cow<'_, B>[src]

Creates an owned Cow<'a, B> with the default value for the contained owned value.

impl<H> Default for BuildHasherDefault<H>[src]

impl<Idx> Default for Range<Idx> where
    Idx: Default, [src]

impl<K, V> Default for BTreeMap<K, V> where
    K: Ord, [src]

pub fn default() -> BTreeMap<K, V>[src]

Creates an empty BTreeMap.

impl<T> Default for Cell<T> where
    T: Default, [src]

pub fn default() -> Cell<T>[src]

Creates a Cell<T>, with the Default value for T.

impl<T> Default for RefCell<T> where
    T: Default, [src]

pub fn default() -> RefCell<T>[src]

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

impl<T> Default for UnsafeCell<T> where
    T: Default, [src]

pub fn default() -> UnsafeCell<T>[src]

Creates an UnsafeCell, with the Default value for T.

impl<T> Default for BTreeSet<T> where
    T: Ord, [src]

pub fn default() -> BTreeSet<T>[src]

Creates an empty BTreeSet.

impl<T> Default for VecDeque<T>[src]

pub fn default() -> VecDeque<T>[src]

Creates an empty VecDeque<T>.

impl<T> Default for Empty<T>[src]

impl<T> Default for PhantomData<T> where
    T: ?Sized, [src]

impl<T> Default for ManuallyDrop<T> where
    T: Default + ?Sized, [src]

impl<T> Default for Wrapping<T> where
    T: Default, [src]

impl<T> Default for Box<[T], Global>[src]

impl<T> Default for Box<T, Global> where
    T: Default, [src]

pub fn default() -> Box<T, Global>ⓘ

Notable traits for Box<R, Global>

impl<R> Read for Box<R, Global> where
    R: Read + ?Sized, impl<W> Write for Box<W, Global> where
    W: Write + ?Sized, impl<I, A> Iterator for Box<I, A> where
    A: Allocator,
    I: Iterator + ?Sized,  type Item = <I as Iterator>::Item;impl<F, A> Future for Box<F, A> where
    A: Allocator + 'static,
    F: Unpin + Future + ?Sized,  type Output = <F as Future>::Output;
[src]

Creates a Box<T>, with the Default value for T.

impl<T> Default for Reverse<T> where
    T: Default, [src]

impl<T> Default for Vec<T, Global>[src]

pub fn default() -> Vec<T, Global>ⓘ

Notable traits for Vec<u8, Global>

impl Write for Vec<u8, Global>
[src]

Creates an empty Vec<T>.

impl<T> Default for Rc<T> where
    T: Default, [src]

pub fn default() -> Rc<T>[src]

Creates a new Rc<T>, with the Default value for T.

Examples

use std::rc::Rc;

let x: Rc<i32> = Default::default();
assert_eq!(*x, 0);

impl<T> Default for sp_std::rc::Weak<T>[src]

pub fn default() -> Weak<T>[src]

Constructs a new Weak<T>, allocating memory for T without initializing it. Calling upgrade on the return value always gives None.

Examples

use std::rc::Weak;

let empty: Weak<i64> = Default::default();
assert!(empty.upgrade().is_none());

impl<T> Default for AtomicPtr<T>[src]

pub fn default() -> AtomicPtr<T>[src]

Creates a null AtomicPtr<T>.

impl<T> Default for Arc<T> where
    T: Default, [src]

pub fn default() -> Arc<T>[src]

Creates a new Arc<T>, with the Default value for T.

Examples

use std::sync::Arc;

let x: Arc<i32> = Default::default();
assert_eq!(*x, 0);

impl<T> Default for Mutex<T> where
    T: Default + ?Sized, [src]

pub fn default() -> Mutex<T>[src]

Creates a Mutex<T>, with the Default value for T.

impl<T> Default for RwLock<T> where
    T: Default, [src]

pub fn default() -> RwLock<T>[src]

Creates a new RwLock<T>, with the Default value for T.

impl<T> Default for sp_std::sync::Weak<T>[src]

pub fn default() -> Weak<T>[src]

Constructs a new Weak<T>, without allocating memory. Calling upgrade on the return value always gives None.

Examples

use std::sync::Weak;

let empty: Weak<i64> = Default::default();
assert!(empty.upgrade().is_none());
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