Trait scrypto::prelude::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 scrypto::prelude::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 BlueprintType

impl Default for FunctionAuth

impl Default for MethodAuthTemplate

impl Default for OwnerRole

impl Default for WithdrawStrategy

impl Default for Level

impl Default for OuterObjectInfo

impl Default for PackageRoyaltyConfig

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 GenericArgs

impl Default for EpochChangeCondition

impl Default for AuthConfig

impl Default for BlueprintDefinitionInit

impl Default for BlueprintVersion

impl Default for PackageDefinition

impl Default for StaticRoleDefinition

impl Default for BurnRoles<Option<AccessRule>>

impl Default for DepositRoles<Option<AccessRule>>

impl Default for FreezeRoles<Option<AccessRule>>

impl Default for FungibleResourceRoles

impl Default for MintRoles<Option<AccessRule>>

impl Default for NonFungibleDataUpdateRoles<Option<AccessRule>>

impl Default for NonFungibleResourceRoles

impl Default for RecallRoles<Option<AccessRule>>

impl Default for RoleAssignmentInit

impl Default for RoleList

impl Default for VaultFrozenFlag

impl Default for WithdrawRoles<Option<AccessRule>>

impl Default for Decimal

impl Default for I192

impl Default for I256

impl Default for I320

impl Default for I384

impl Default for I448

impl Default for I512

impl Default for I768

impl Default for PreciseDecimal

impl Default for U192

impl Default for U256

impl Default for U320

impl Default for U384

impl Default for U448

impl Default for U512

impl Default for U768

impl Default for Metadata

impl Default for Royalty

impl Default for FungibleResourceType

impl Default for BlueprintEventSchemaInit

impl Default for BlueprintFunctionsSchemaInit

impl Default for BlueprintHooksInit

§`enum`s

§How can I implement `Default`?