loam_sdk::soroban_sdk::testutils::arbitrary::std::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 &OsStr

impl Default for &mut str

impl Default for AsciiChar

impl Default for SWFlags

impl Default for TEFlags

impl Default for TagMode

impl Default for PrefilterConfig

impl Default for serde_json::value::Value

§Examples

impl Default for DiagnosticLevel

impl Default for FootprintMode

impl Default for FuelConsumptionMode

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 Env

impl Default for SymbolStr

impl Default for Val

impl Default for ContractCostParams

impl Default for DataValue

impl Default for DiagnosticEvents

impl Default for EncryptedBody

impl Default for LedgerEntryChanges

impl Default for PeerStatList

impl Default for ProofLevel

impl Default for ScBytes

impl Default for ScMap

impl Default for ScString

impl Default for ScSymbol

impl Default for ScVec

impl Default for Signature

impl Default for String32

impl Default for String64

impl Default for TimeSlicedPeerDataList

impl Default for TxAdvertVector

impl Default for TxDemandVector

impl Default for UpgradeType

impl Default for loam_sdk::soroban_sdk::xdr::Value

impl Default for AuthSnapshot

impl Default for EnvTestConfig

impl Default for EventsSnapshot

impl Default for Generators

impl Default for LedgerInfo

impl Default for Snapshot

impl Default for Global

impl Default for System

impl Default for Box<str>

impl Default for Box<CStr>

impl Default for Box<OsStr>

impl Default for ByteString

Trait Default

§`enum`s

§How can I implement `Default`?