rosetta_server::crypto::bip39::core::default

Trait Default

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 primitive 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 }
}

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Default

Trait Default Copy item path

§Derivable

§enums

§How can I implement Default?

§Examples

Required Methods§

fn default() -> Self

§Examples

Dyn Compatibility§

Implementors§

impl Default for &serde_json::value::Value

impl Default for &str

impl Default for &CStr

impl Default for &std::ffi::os_str::OsStr

impl Default for &StyledStr

impl Default for &Styles

impl Default for &DataLocale

impl Default for &DataMarkerAttributes

impl Default for &mut str

impl Default for BlockEventType

impl Default for Case

impl Default for CoinAction

impl Default for CurveType

impl Default for Direction

impl Default for ExemptionType

impl Default for Operator

impl Default for SignatureType

impl Default for Language

impl Default for AsciiChar

impl Default for Action

impl Default for State

impl Default for LineEnding

impl Default for BigEndian

impl Default for LittleEndian

impl Default for ValueHint

impl Default for clap_builder::util::color::ColorChoice

impl Default for colorchoice::ColorChoice

impl Default for TagMode

impl Default for PollNext

impl Default for BidiPairedBracketType

impl Default for PrefilterConfig

impl Default for serde_json::value::Value

§Examples

impl Default for Sign

impl Default for MissedTickBehavior

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 AccountBalanceRequest

impl Default for AccountBalanceResponse

impl Default for AccountCoinsRequest

impl Default for AccountCoinsResponse

impl Default for AccountFaucetRequest

impl Default for AccountIdentifier

impl Default for Allow

impl Default for Amount

impl Default for BalanceExemption

impl Default for Block

impl Default for BlockEvent

impl Default for BlockIdentifier

impl Default for BlockRequest

impl Default for BlockResponse

impl Default for BlockTransaction

Trait Default

§`enum`s

§How can I implement `Default`?