Trait gclient::ext::sp_core::sp_std::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.

§`enum`s

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.

The #[default] attribute was stabilized in Rust 1.62.0.

§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§

1.0.0 · source

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 }
}

1.9.0 · source§

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

1.0.0 · source§

impl Default for ExitCode

The default value is ExitCode::SUCCESS

1.73.0 · source§

impl Default for ExitStatus

The default value is one which indicates successful completion.

Returns a Uri representing /

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);

§

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 desireable 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);

§

impl Default for ColorChoice

impl Default for End

Creates a modifier used to represent the end of input.

Creates a modifier that indicates the value is padded with zeroes and has the 24-hour representation.

impl Default for MonthRepr

Creates a modifier that indicates the value uses the Numerical representation.

impl Default for OffsetMinute

Creates a modifier that indicates the value is padded with zeroes.

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impl Default for OffsetSecond

Creates a modifier that indicates the value is padded with zeroes.

Creates a modifier that indicates the value is padded with zeroes.

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impl Default for Padding

impl Default for PatternID

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impl Default for Period

Creates a modifier that indicates the value uses the upper-case representation and is case-sensitive when parsing.

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.

§

impl Default for SubsecondDigits

Creates a modifier that indicates the stringified value contains one or more digits.

§

impl Default for UnixTimestampPrecision

Creates a modifier that indicates the value represents the number of seconds since the Unix epoch.

Returns a Uri representing /

Creates a modifier that indicates that the value is padded with zeroes and uses the Iso representation.

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impl Default for WeekNumberRepr

Creates a modifier that indicates that the value uses the Iso representation.

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impl Default for Weekday

Creates a modifier that indicates the value uses the Long representation and is case-sensitive when parsing. If the representation is changed to a numerical one, the instance defaults to one-based indexing.

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impl Default for WeekdayRepr

Creates a modifier that indicates the value uses the Long representation.

impl Default for YearRepr

Creates a modifier that indicates the value uses the Full representation.

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

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.

§

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

Trait gclient::ext::sp_core::sp_std::default::DefaultCopy item path

§Derivable

§enums

§How can I implement Default?

§Examples

Required Methods§

fn default() -> Self

§Examples

Object Safety§

Implementors§

impl Default for &str

impl Default for &CStr

impl Default for &OsStr

impl Default for &mut str

impl Default for DispatchKind

impl Default for ErrorReplyReason

impl Default for ReplyCode

impl Default for SignalCode

impl Default for SimpleExecutionError

impl Default for SimpleProgramCreationError

impl Default for SuccessReplyReason

impl Default for ExtrinsicInclusionMode

impl Default for RuntimeString

impl Default for StateVersion

impl Default for AsciiChar

impl Default for Value

§Examples

impl Default for bool

impl Default for char

impl Default for f16

impl Default for f32

impl Default for f64

impl Default for f128

impl Default for i8

impl Default for i16

impl Default for i32

impl Default for i64

impl Default for i128

impl Default for isize

impl Default for u8

impl Default for u16

impl Default for u32

impl Default for u64

impl Default for u128

impl Default for ()

impl Default for usize

impl Default for RuntimeBufferSizeError

impl Default for TryNewCodeConfig

impl Default for BlocksAmount

impl Default for BytesAmount

impl Default for CallsAmount

impl Default for ExtCosts

impl Default for InstantiationCosts

impl Default for LazyPagesCosts

impl Default for ProcessCosts

impl Default for RentCosts

impl Default for SyscallCosts

impl Default for GasInfo

impl Default for CustomConstantCostRules

impl Default for DbWeights

impl Default for InstantiationWeights

impl Default for InstructionWeights

impl Default for Limits

impl Default for MemoryWeights

impl Default for RentWeights

impl Default for Schedule

impl Default for SyscallWeights

impl Default for TaskWeights

impl Default for IntoPageBufError

impl Default for Message

impl Default for ReplyDetails

impl Default for SignalDetails

impl Default for ContextOutcome

impl Default for ContextSettings

impl Default for ContextStore

impl Default for HandleMessage

impl Default for HandlePacket

impl Default for IncomingDispatch

impl Default for IncomingMessage

impl Default for InitMessage

Trait gclient::ext::sp_core::sp_std::default::Default

§`enum`s

§How can I implement `Default`?