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.

§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§

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 }
}

Object Safety§

This trait is not object safe.

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

§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 RuntimeString

impl Default for StateVersion

impl Default for Value

§Examples

impl Default for bool

impl Default for char

impl Default for f32

impl Default for f64

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 SyscallCosts

impl Default for GasInfo

impl Default for CodeId

impl Default for MessageId

impl Default for ProgramId

impl Default for ReservationId

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

impl Default for InitPacket

impl Default for ReplyMessage

impl Default for ReplyPacket

impl Default for SignalMessage

impl Default for StoredMessage

impl Default for PayloadSizeError

impl Default for UserMessage

impl Default for UserStoredMessage

impl Default for MemoryInfix

impl Default for ReservationNonce

impl Default for gsdk::backtrace::Backtrace

impl Default for Signature

impl Default for gclient::ext::sp_runtime::biguint::BigUint

impl Default for Time

impl Default for gclient::ext::sp_runtime::offchain::Duration

impl Default for OpaqueNetworkState

§`enum`s

§How can I implement `Default`?