Trait sgx_tstd::default::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 sgx_tstd::default::Default

Required Methods§

fn default() -> Self

Object Safety§

Implementors§

impl Default for &str

impl Default for &CStr

impl Default for &OsStr

impl Default for &mut str

impl Default for MapAddr

impl Default for FutexClockId

impl Default for FutexOp

impl Default for PageType

impl Default for Feature

impl Default for Version

impl Default for ExceptionType

impl Default for ExceptionVector

impl Default for HandleResult

impl Default for PceError

impl Default for QcnlError

impl Default for Quote3Error

impl Default for SgxStatus

impl Default for DirIndex

impl Default for EcResult

impl Default for RsaKeyType

impl Default for RsaResult

impl Default for PckCertFlag

impl Default for ProdType

impl Default for QeType

impl Default for QlAttestationAlgorithmId

impl Default for QlCertKeyType

impl Default for QlConfigVersion

impl Default for QlLogLevel

impl Default for QlPathType

impl Default for QlQvResult

impl Default for QlRequestPolicy

impl Default for QvPathType

impl Default for DhSessionRole

impl Default for EnclaveMode

impl Default for KeyName

impl Default for ProtectPerm

impl Default for RaKeyType

impl Default for QuoteSignType

impl Default for SwitchlessWokerEvent

impl Default for SwitchlessWokerType

impl Default for SgxDeviceStatus

impl Default for TcsPolicy

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 AlignReq

impl Default for CpuidResult

impl Default for AddrInfoHints

impl Default for MsgHdrFlags

impl Default for sgx_sync::condvar::Condvar

impl Default for FutexFlags

impl Default for MovableMutex

impl Default for MovableRwLock

impl Default for PageFlags

impl Default for PageInfo

impl Default for Rng

impl Default for AlignKeyRequest

impl Default for AlignReport2Mac

impl Default for AlignReport

impl Default for AlignReportData

impl Default for AlignTargetInfo