Trait gstd::prelude::default::Default

1.0.0 · source ·
pub trait Default: Sized {
    // Required method
    fn default() -> Self;
}
Expand description

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.

§enums

When using #[derive(Default)] on an enum, you need to choose which unit variant will be default. You do this by placing the #[default] attribute on the variant.

#[derive(Default)]
enum Kind {
    #[default]
    A,
    B,
    C,
}

You cannot use the #[default] attribute on non-unit or non-exhaustive variants.

§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§

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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();

Making your own:

enum Kind {
    A,
    B,
    C,
}

impl Default for Kind {
    fn default() -> Self { Kind::A }
}

Object Safety§

This trait is not object safe.

Implementors§

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impl Default for &str

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impl Default for &CStr

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impl Default for &OsStr

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impl Default for &mut str

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impl Default for ErrorReplyReason

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impl Default for ReplyCode

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impl Default for SignalCode

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impl Default for SimpleExecutionError

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impl Default for SimpleProgramCreationError

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impl Default for SuccessReplyReason

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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 ()

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impl Default for usize

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impl Default for gstd::ActorId

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impl Default for gstd::CodeId

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impl Default for gstd::MessageId

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impl Default for Reservations

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impl Default for CString

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impl Default for Error

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impl Default for SipHasher

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impl Default for PhantomPinned

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impl Default for RangeFull

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impl Default for Alignment

Returns Alignment::MIN, which is valid for any type.

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impl Default for gstd::prelude::Box<str>

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impl Default for gstd::prelude::Box<CStr>

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impl Default for gstd::prelude::Box<OsStr>

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impl Default for String

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impl Default for Duration

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impl Default for alloc::alloc::Global

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impl Default for AtomicBool

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impl Default for AtomicI8

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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 AtomicIsize

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impl Default for AtomicU8

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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 AtomicUsize

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impl Default for System

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impl Default for OsString

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impl Default for FileTimes

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impl Default for DefaultHasher

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impl Default for std::hash::random::RandomState

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impl Default for std::io::util::Empty

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impl Default for Sink

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impl Default for PathBuf

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impl Default for ExitCode

The default value is ExitCode::SUCCESS

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impl Default for ExitStatus

The default value is one which indicates successful completion.

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impl Default for Condvar

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impl Default for IgnoredAny

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impl Default for ThreadRng

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impl Default for OsRng

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impl Default for AHasher

Provides a default Hasher with fixed keys. This is typically used in conjunction with BuildHasherDefault to create [AHasher]s in order to hash the keys of the map.

Generally it is preferable to use [RandomState] instead, so that different hashmaps will have different keys. However if fixed keys are desirable this may be used instead.

§Example

use std::hash::BuildHasherDefault;
use ahash::{AHasher, RandomState};
use std::collections::HashMap;

let mut map: HashMap<i32, i32, BuildHasherDefault<AHasher>> = HashMap::default();
map.insert(12, 34);
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impl Default for ActorId

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impl Default for AtomicWaker

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impl Default for BigEndian

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impl Default for BlockNumberWithHash

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impl Default for Bytes

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impl Default for BytesMut

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impl Default for CodeId

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impl Default for Const

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impl Default for ErrorBytes

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impl Default for ErrorWithGas

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impl Default for ErrorWithHandle

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impl Default for ErrorWithHash

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impl Default for ErrorWithReplyCode

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impl Default for ErrorWithSignalCode

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impl Default for ErrorWithTwoHashes

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impl Default for FinderBuilder

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impl Default for Global

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impl Default for H128

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impl Default for H160

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impl Default for H256

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impl Default for H384

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impl Default for H512

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impl Default for H768

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impl Default for HashWithValue

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impl Default for LittleEndian

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impl Default for LocalPool

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impl Default for Lsb0

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impl Default for MessageId

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impl Default for Msb0

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impl Default for Mut

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impl Default for NullPtrError

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impl Default for OnceBool

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impl Default for OnceNonZeroUsize

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impl Default for PollNext

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impl Default for PortableRegistryBuilder

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impl Default for Prefilter

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impl Default for RandomState

Creates an instance of RandomState using keys obtained from the random number generator. Each instance created in this way will have a unique set of keys. (But the resulting instance can be used to create many hashers each or which will have the same keys.)

This is the same as [RandomState::new()]

NOTE: For safety this trait impl is only available available if either of the flags runtime-rng (on by default) or compile-time-rng are enabled. This is to prevent weakly keyed maps from being accidentally created. Instead one of constructors for [RandomState] must be used.

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impl Default for Registry

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impl Default for ReservationId

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impl Default for ThreadPoolBuilder

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impl Default for TwoHashes

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impl Default for TwoHashesWithValue

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impl Default for U128

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impl Default for U256

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impl Default for U512

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impl Default for vec128_storage

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impl Default for vec256_storage

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impl Default for vec512_storage

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impl<'a, K, V> Default for gstd::prelude::collections::btree_map::Iter<'a, K, V>
where K: 'a, V: 'a,

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impl<'a, K, V> Default for gstd::prelude::collections::btree_map::IterMut<'a, K, V>
where K: 'a, V: 'a,

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impl<'a, M, T, O> Default for BitDomain<'a, M, T, O>
where M: Mutability, T: 'a + BitStore, O: BitOrder, Address<M, BitSlice<T, O>>: Referential<'a>, Address<M, BitSlice<<T as BitStore>::Unalias, O>>: Referential<'a>, <Address<M, BitSlice<T, O>> as Referential<'a>>::Ref: Default, <Address<M, BitSlice<<T as BitStore>::Unalias, O>> as Referential<'a>>::Ref: Default,

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impl<'a, M, T, O> Default for Domain<'a, M, T, O>
where M: Mutability, T: 'a + BitStore, O: BitOrder, Address<M, T>: Referential<'a>, Address<M, [<T as BitStore>::Unalias]>: SliceReferential<'a>, <Address<M, [<T as BitStore>::Unalias]> as Referential<'a>>::Ref: Default,

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impl<'a, T> Default for OnceRef<'a, T>

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impl<A> Default for Box<str, A>
where A: Allocator + Default,

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impl<A, B> Default for Chain<A, B>
where A: Default, B: Default,

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impl<A, O> Default for BitArray<A, O>
where A: BitViewSized, O: BitOrder,

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

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impl<F> Default for OptionFuture<F>

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impl<F> Default for Variants<F>
where F: Default + Form,

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impl<F, N, T> Default for FieldBuilder<F, N, T>
where F: Form,

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impl<F, S> Default for TypeBuilder<F, S>
where F: Form,

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impl<F, T> Default for FieldsBuilder<F, T>
where F: Form,

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impl<Fut> Default for FuturesOrdered<Fut>
where Fut: Future,

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impl<Fut> Default for FuturesUnordered<Fut>

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impl<H> Default for BuildHasherDefault<H>

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impl<I> Default for Cloned<I>
where I: Default,

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impl<I> Default for Copied<I>
where I: Default,

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impl<I> Default for Enumerate<I>
where I: Default,

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impl<I> Default for Flatten<I>
where I: Default + Iterator, <I as Iterator>::Item: IntoIterator,

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impl<I> Default for Fuse<I>
where I: Default,

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impl<I> Default for Rev<I>
where I: Default,

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impl<Idx> Default for gstd::prelude::ops::Range<Idx>
where Idx: Default,

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impl<Inner> Default for Frozen<Inner>
where Inner: Default + Mutability,

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impl<K, V> Default for Keys<'_, K, V>

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impl<K, V> Default for gstd::prelude::collections::btree_map::Range<'_, K, V>

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impl<K, V> Default for Values<'_, K, V>

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impl<K, V> Default for BTreeMap<K, V>

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impl<K, V> Default for AHashMap<K, V>

NOTE: For safety this trait impl is only available available if either of the flags runtime-rng (on by default) or compile-time-rng are enabled. This is to prevent weakly keyed maps from being accidentally created. Instead one of constructors for [RandomState] must be used.

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impl<K, V, A> Default for gstd::prelude::collections::btree_map::IntoIter<K, V, A>
where A: Allocator + Default + Clone,

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impl<K, V, A> Default for IntoKeys<K, V, A>
where A: Allocator + Default + Clone,

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impl<K, V, A> Default for IntoValues<K, V, A>
where A: Allocator + Default + Clone,

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impl<K, V, S> Default for std::collections::hash::map::HashMap<K, V, S>
where S: Default,

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impl<K, V, S, A> Default for gstd::prelude::collections::HashMap<K, V, S, A>
where S: Default, A: Default + Allocator,

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impl<M, T, O> Default for BitPtrRange<M, T, O>
where M: Mutability, T: BitStore, O: BitOrder,

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impl<R> Default for BitEnd<R>
where R: Default + BitRegister,

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impl<R> Default for BitIdx<R>
where R: Default + BitRegister,

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impl<R> Default for BitIdxError<R>
where R: Default + BitRegister,

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impl<R> Default for BitMask<R>
where R: Default + BitRegister,

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impl<R> Default for BitPos<R>
where R: Default + BitRegister,

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impl<R> Default for BitSel<R>
where R: Default + BitRegister,

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impl<St> Default for SelectAll<St>
where St: Stream + Unpin,

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impl<T> Default for &[T]

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impl<T> Default for &mut [T]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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impl<T> Default for (T₁, T₂, …, Tₙ)
where T: Default,

This trait is implemented for tuples up to twelve items long.

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impl<T> Default for Cell<T>
where T: Default,

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impl<T> Default for LazyCell<T>
where T: Default,

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impl<T> Default for gstd::prelude::cell::OnceCell<T>

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impl<T> Default for RefCell<T>
where T: Default,

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impl<T> Default for SyncUnsafeCell<T>
where T: Default,

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impl<T> Default for UnsafeCell<T>
where T: Default,

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impl<T> Default for Reverse<T>
where T: Default,

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impl<T> Default for gstd::prelude::collections::binary_heap::IntoIter<T>

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impl<T> Default for gstd::prelude::collections::btree_set::Iter<'_, T>

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impl<T> Default for gstd::prelude::collections::btree_set::Range<'_, T>

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impl<T> Default for gstd::prelude::collections::linked_list::IntoIter<T>

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impl<T> Default for gstd::prelude::collections::linked_list::Iter<'_, T>

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impl<T> Default for gstd::prelude::collections::linked_list::IterMut<'_, T>

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impl<T> Default for BTreeSet<T>

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impl<T> Default for BinaryHeap<T>
where T: Ord,

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impl<T> Default for LinkedList<T>

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impl<T> Default for VecDeque<T>

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impl<T> Default for gstd::prelude::iter::Empty<T>

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

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

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impl<T> Default for Saturating<T>
where T: Default,

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impl<T> Default for Wrapping<T>
where T: Default,

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impl<T> Default for AssertUnwindSafe<T>
where T: Default,

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impl<T> Default for Rc<T>
where T: Default,

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impl<T> Default for gstd::prelude::rc::Weak<T>

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impl<T> Default for gstd::prelude::slice::Iter<'_, T>

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impl<T> Default for gstd::prelude::slice::IterMut<'_, T>

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impl<T> Default for gstd::prelude::Box<[T]>

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impl<T> Default for gstd::prelude::Box<T>
where T: Default,

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impl<T> Default for gstd::prelude::Vec<T>

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impl<T> Default for Arc<T>
where T: Default,

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impl<T> Default for alloc::sync::Weak<T>

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impl<T> Default for AtomicPtr<T>

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impl<T> Default for Exclusive<T>
where T: Default + ?Sized,

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impl<T> Default for std::io::cursor::Cursor<T>
where T: Default,

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impl<T> Default for LazyLock<T>
where T: Default,

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impl<T> Default for std::sync::mutex::Mutex<T>
where T: Default + ?Sized,

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impl<T> Default for OnceLock<T>

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impl<T> Default for std::sync::rwlock::RwLock<T>
where T: Default,

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impl<T> Default for AHashSet<T>

NOTE: For safety this trait impl is only available available if either of the flags runtime-rng (on by default) or compile-time-rng are enabled. This is to prevent weakly keyed maps from being accidentally created. Instead one of constructors for [RandomState] must be used.

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impl<T> Default for Box<T>
where T: Default,

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impl<T> Default for Cursor<T>
where T: Default,

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impl<T> Default for Interner<T>
where T: Ord,

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impl<T> Default for Lazy<T>
where T: Default,

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impl<T> Default for Lazy<T>
where T: Default,

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impl<T> Default for Mutex<T>
where T: Default,

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impl<T> Default for OnceBox<T>

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impl<T> Default for OnceCell<T>

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impl<T> Default for OnceCell<T>

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impl<T> Default for Path<T>
where T: Form,

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impl<T> Default for Slab<T>

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impl<T> Default for Unalign<T>
where T: Default,

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impl<T> Default for Vec<T>

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impl<T, A> Default for gstd::prelude::collections::btree_set::IntoIter<T, A>
where A: Allocator + Default + Clone,

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impl<T, A> Default for gstd::prelude::vec::IntoIter<T, A>
where A: Allocator + Default,

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impl<T, A> Default for Box<[T], A>
where A: Allocator + Default,

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impl<T, A> Default for HashTable<T, A>
where A: Allocator + Default,

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impl<T, A> Default for RawTable<T, A>
where A: Allocator + Default,

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impl<T, O> Default for &BitSlice<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Default for &mut BitSlice<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Default for BitBox<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Default for BitVec<T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Default for IterOnes<'_, T, O>
where T: BitStore, O: BitOrder,

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impl<T, O> Default for IterZeros<'_, T, O>
where T: BitStore, O: BitOrder,

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impl<T, S> Default for std::collections::hash::set::HashSet<T, S>
where S: Default,

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impl<T, S, A> Default for gstd::prelude::collections::HashSet<T, S, A>
where S: Default, A: Default + Allocator,

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impl<T, const CAP: usize> Default for ArrayVec<T, CAP>

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impl<T, const N: usize> Default for Mask<T, N>

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impl<T, const N: usize> Default for Simd<T, N>

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impl<T: Default> Default for gstd::sync::Mutex<T>

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impl<T: Default> Default for gstd::sync::RwLock<T>

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impl<const CAP: usize> Default for ArrayString<CAP>