flams_router_vscode::server_fn::inventory::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 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 }
}

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.

Implementors§

Source §

impl Default for &serde_json::value::Value

1.0.0 (const: unstable) · Source§

impl Default for &str

1.10.0 · Source§

impl Default for &DataLocale

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impl Default for &DataMarkerAttributes

1.28.0 (const: unstable) · Source§

impl Default for ReloadWSProtocol

1.0.0 (const: unstable) · Source§

impl Default for RemoteRedirect

Source §

impl Default for serde_json::value::Value

The default value is Value::Null.

This is useful for handling omitted Value fields when deserializing.

§Examples

use serde_json::Value;

#[derive(Deserialize)]
struct Settings {
    level: i32,
    #[serde(default)]
    extras: Value,
}

let data = r#" { "level": 42 } "#;
let s: Settings = serde_json::from_str(data)?;

assert_eq!(s.level, 42);
assert_eq!(s.extras, Value::Null);

impl Default for proc_macro::TokenStream

1.28.0 · Source§

impl Default for DefaultHasher

1.7.0 · Source§

impl Default for std::hash::random::RandomState

1.0.0 · 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.

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 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 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 MissedTickBehavior

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impl Default for MmapOptions

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impl Default for Month

Creates an instance of this type that indicates the value uses the Numerical representation, is padded with zeroes, and is case-sensitive when parsing.

§

impl Default for MonthRepr

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

Creates a modifier that indicates the value only uses a sign for negative values and is padded with zeroes.

§

impl Default for OffsetMinute

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

§

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.

§

impl Default for Other

§

impl Default for OutlineStyle

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impl Default for Padding

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

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

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

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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.

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 WhichCaptures

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impl Default for WhitespaceTokenizer

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impl Default for XAttrs

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impl Default for Year

Creates a modifier that indicates the value uses the Full representation, is padded with zeroes, uses the Gregorian calendar as its base, and only includes the year’s sign if necessary.

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impl Default for YearMonthDuration

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impl Default for YearRange

Creates a modifier that indicates the value uses the Extended range.

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impl Default for YearRepr

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

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Trait DefaultCopy 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 &DataLocale

impl Default for &DataMarkerAttributes

impl Default for &mut str

impl Default for ArgMode

impl Default for Language

impl Default for flams_web_utils::components::drawer::DrawerSize

impl Default for flams_web_utils::components::spinner::SpinnerSize

impl Default for ThemeType

impl Default for Env

impl Default for ReloadWSProtocol

impl Default for AsciiChar

impl Default for RemoteRedirect

impl Default for IpNet

impl Default for serde_json::value::Value

§Examples

impl Default for PathArguments

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 GLInstance

impl Default for ArgSpec

impl Default for FileStateSummary

impl Default for DocumentStyles

impl Default for QueryFilter

impl Default for ArchiveManager

impl Default for FileStates

impl Default for SourceDir

impl Default for ArchiveTree

impl Default for RDFStore

impl Default for TemporaryBackend

impl Default for IdCounter

impl Default for LogTree

impl Default for BuildQueueSettings

impl Default for GitlabSettings

impl Default for ServerSettings

impl Default for SettingsSpec

impl Default for ByteOffset

impl Default for LSPLineCol

impl Default for Delta

impl Default for Eta

impl Default for Timestamp

impl Default for Indentor<'_>

impl Default for CssIds

impl Default for ArcTrigger

impl Default for ErrorId

impl Default for flams_router_vscode::Errors

impl Default for Nonce

impl Default for Owner

impl Default for SuppressResourceLoad

impl Default for TextProp

Trait Default

§`enum`s

§How can I implement `Default`?