kvarn::prelude::utils::prelude::compact_str::core::prelude::rust_2021

Trait Default

1.55.0 · 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.

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§

1.55.0 · 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§

1.0.0 · source§

impl Default for &str

1.10.0 · source§

impl Default for &mut str

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impl Default for PreferredCompression

1.0.0 · source§

impl Default for i8

1.0.0 · source§

impl Default for u8

1.0.0 · source§

impl Default for ()

1.0.0 · source§

impl Default for AllowList

The default cache_for is 1 hour.

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impl Default for Rule

Gives content-security-policy: default-src 'self'; style-src 'self' 'unsafe-inline'.

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impl Default for Plugins

Available on crate feature handover only.

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impl Default for kvarn::extensions::Extensions

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impl Default for LimitManager

Default is Self::new(10, 10, 10).

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impl Default for kvarn::prelude::fs::OpenOptions

1.80.0 · source§

impl Default for kvarn::prelude::Arc<str>

Available on non-no_global_oom_handling only.

1.80.0 · source§

impl Default for kvarn::prelude::Arc<CStr>

Available on non-no_global_oom_handling only.

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impl Default for CompactString

1.3.0 · source§

impl Default for kvarn::prelude::Duration

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impl Default for kvarn::prelude::Version

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impl Default for WriteableBytes

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impl Default for kvarn::prelude::utils::prelude::io::Empty

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impl Default for kvarn::prelude::utils::prelude::uri::Builder

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impl Default for PhantomPinned

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impl Default for Alignment

Returns Alignment::MIN, which is valid for any type.

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impl Default for AtomicBool

Available on target_has_atomic_load_store="8" only.

1.34.0 · source§

impl Default for Box<str>

Available on non-no_global_oom_handling only.

1.17.0 · source§

impl Default for Rc<str>

Available on non-no_global_oom_handling only.

1.80.0 · source§

impl Default for Rc<CStr>

Available on non-no_global_oom_handling only.

1.0.0 · source§

impl Default for DefaultHasher

1.7.0 · 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.

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impl Default for DefaultRandomSource

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impl Default for Day

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

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impl Default for DecompressorOxide

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impl Default for DirBuilder

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impl Default for DirBuilder

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impl Default for Dispatch

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impl Default for Duration

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impl Default for EC_builtin_curve

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impl Default for EDIPartyName_st

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impl Default for Eager

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impl Default for EmptyIVec

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impl Default for End

Creates a modifier used to represent the end of input.

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impl Default for EndpointConfig

Available on crate feature ring only.

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impl Default for Event

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impl Default for EventAttributes

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impl Default for EventKind

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impl Default for EvictionPolicy

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impl Default for Extensions

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impl Default for FinderBuilder

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impl Default for FnvHasher

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impl Default for FormatterOptions

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impl Default for FrameHeader

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impl Default for FrameStats

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impl Default for FutexWaitV

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impl Default for FxBuildHasher

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impl Default for FxHasher

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impl Default for GENERAL_NAME_st

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impl Default for GENERAL_NAME_st__bindgen_ty_1

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impl Default for GENERAL_SUBTREE_st

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impl Default for GeneralPurposeConfig

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impl Default for H9Opts

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impl Default for HRSS_private_key

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impl Default for HRSS_public_key

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impl Default for HashedConnectionIdGenerator

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impl Default for Hasher

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impl Default for HistogramCommand

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impl Default for HistogramDistance

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impl Default for HistogramLiteral

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impl Default for HistogramPair

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impl Default for Hour

Creates a modifier that indicates the value is padded with zeroes and has the 24-hour representation.

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impl Default for HuffmanCode

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impl Default for HuffmanTree

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impl Default for ISSUING_DIST_POINT_st

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impl Default for IdleTimeout

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impl Default for InflateState

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impl Default for InvalidBufferSize

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impl Default for InvalidOutputSize

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impl Default for Iv

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impl Default for Lazy

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impl Default for LengthDelimitedCodec

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impl Default for LinesCodec

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impl Default for LiteralBlockSwitch

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impl Default for LiteralPredictionModeNibble

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impl Default for LittleEndian

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impl Default for LocalPool

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impl Default for LocalSet

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impl Default for Minute

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

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impl Default for MissedTickBehavior

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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.

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impl Default for MonthRepr

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

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impl Default for MtuDiscoveryConfig

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impl Default for MultiThreadedSpawner

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impl Default for NAME_CONSTRAINTS_st

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impl Default for NOTICEREF_st

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impl Default for Netscape_spkac_st

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impl Default for Netscape_spki_st

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impl Default for NewRenoConfig

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impl Default for NoSubscriber

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impl Default for Notify

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impl Default for Null

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impl Default for OffsetHour

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

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impl Default for OffsetMinute

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

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impl Default for OffsetSecond

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

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impl Default for Once

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impl Default for OnceBool

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impl Default for OnceNonZeroUsize

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impl Default for OpenHow

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impl Default for OpenOptions

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impl Default for OpenOptions

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impl Default for Ordinal

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

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impl Default for PDF

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impl Default for POLICYINFO_st

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impl Default for POLICYQUALINFO_st

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impl Default for POLICYQUALINFO_st__bindgen_ty_1

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impl Default for POLICY_CONSTRAINTS_st

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impl Default for POLICY_MAPPING_st

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impl Default for Padding

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

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impl Default for Parker

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impl Default for Parsed

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impl Default for PathStats

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impl Default for Period

Creates a modifier that indicates the value uses the upper-case representation and is case-sensitive when parsing.

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impl Default for PollNext

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impl Default for PrefilterConfig

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impl Default for Probe

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impl Default for RIPEMD160state_st

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impl Default for RandomConnectionIdGenerator

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impl Default for RecoderState

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impl Default for RecvMeta

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impl Default for Resumption

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impl Default for Rng

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impl Default for Second

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

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impl Default for ServerConnectionData

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impl Default for Sha1Core

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impl Default for SingleThreadedSpawner

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impl Default for SliceOffset

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impl Default for SpinWait

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impl Default for StandardAlloc

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impl Default for StartPosQueue

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impl Default for StatxBuilder

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impl Default for Subsecond

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.

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impl Default for SystemRandom

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impl Default for Timespec

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impl Default for TransportConfig

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impl Default for USERNOTICE_st

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impl Default for UdpStats

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impl Default for UnixTimestamp

Creates a modifier that indicates the value represents the number of seconds since the Unix epoch. The sign is not mandatory.

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impl Default for UnixTimestampPrecision

Creates a modifier that indicates the value represents the number of seconds since the Unix epoch.

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impl Default for UnparkResult

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impl Default for Utf8Bytes

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impl Default for VarInt

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impl Default for Version

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impl Default for WaitGroup

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impl Default for WebSocketConfig

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impl Default for WeekNumber

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.

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impl Default for Written

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impl Default for X509_algor_st

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impl Default for X509_info_st

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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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