Trait nom::lib::std::prelude::v1::rust_2021::Default1.0.0[−][src]

pub trait Default {
    pub fn default() -> Self;
}

[−]

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.

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

`pub fn default() -> Self`[src][−]

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 }
}

Trait nom::lib::std::prelude::v1::rust_2021::Default⎘1.0.0[−][src]

Derivable

How can I implement Default?

Examples

Required methods

pub fn default() -> Self[src][−]

Examples

Implementations on Foreign Types

impl<T> Default for PhantomData<T> where T: ?Sized, [src][−]

pub fn default() -> PhantomData<T>[src]

impl Default for AtomicBool[src][−]

pub fn default() -> AtomicBool[src][−]

impl Default for SipHasher[src][−]

pub fn default() -> SipHasher[src]

impl<T> Default for Wrapping<T> where T: Default, [src][−]

pub fn default() -> Wrapping<T>[src]

impl Default for AtomicI8[src][−]

pub fn default() -> AtomicI8[src]

impl<T> Default for Lazy<T, fn() -> T> where T: Default, [src][−]

pub fn default() -> Lazy<T, fn() -> T>[src][−]

impl<T> Default for UnsafeCell<T> where T: Default, [src][−]

pub fn default() -> UnsafeCell<T>[src][−]

impl<T> Default for OnceCell<T>[src][−]

pub fn default() -> OnceCell<T>[src]

impl Default for AtomicU16[src][−]

pub fn default() -> AtomicU16[src]

impl Default for AtomicU64[src][−]

pub fn default() -> AtomicU64[src]

impl Default for Duration[src][−]

pub fn default() -> Duration[src]

impl Default for AtomicU32[src][−]

pub fn default() -> AtomicU32[src]

impl Default for AtomicUsize[src][−]

pub fn default() -> AtomicUsize[src]

impl Default for AtomicI32[src][−]

pub fn default() -> AtomicI32[src]

impl<T> Default for RefCell<T> where T: Default, [src][−]

pub fn default() -> RefCell<T>[src][−]

impl Default for AtomicU8[src][−]

pub fn default() -> AtomicU8[src]

impl Default for PhantomPinned[src][−]

pub fn default() -> PhantomPinned[src]

impl<T> Default for Cell<T> where T: Default, [src][−]

pub fn default() -> Cell<T>[src][−]

impl Default for AtomicIsize[src][−]

pub fn default() -> AtomicIsize[src]

impl Default for AtomicI64[src][−]

pub fn default() -> AtomicI64[src]

impl<H> Default for BuildHasherDefault<H>[src][−]

pub fn default() -> BuildHasherDefault<H>[src]

impl<T> Default for AtomicPtr<T>[src][−]

pub fn default() -> AtomicPtr<T>[src][−]

impl Default for AtomicI16[src][−]

pub fn default() -> AtomicI16[src]

Implementors

impl Default for ()[src][+]

pub fn default()[src][−]

impl Default for Error[src][+]

pub fn default() -> Error[src]

impl Default for RangeFull[src][+]

pub fn default() -> RangeFull[src]

impl Default for bool[src][+]

pub fn default() -> bool[src][−]

impl Default for char[src][+]

pub fn default() -> char[src][−]

impl Default for f32[src][+]

pub fn default() -> f32[src][−]

impl Default for f64[src][+]

pub fn default() -> f64[src][−]

impl Default for i8[src][+]

pub fn default() -> i8[src][−]

impl Default for i16[src][+]

pub fn default() -> i16[src][−]

impl Default for i32[src][+]

pub fn default() -> i32[src][−]

impl Default for i64[src][+]

pub fn default() -> i64[src][−]

impl Default for i128[src][+]

pub fn default() -> i128[src][−]

impl Default for isize[src][+]

Trait nom::lib::std::prelude::v1::rust_2021::Default1.0.0[−][src]

How can I implement `Default`?

`pub fn default() -> Self`[src][−]

`impl<T> Default for PhantomData<T> where T: ?Sized,` [src][−]

`pub fn default() -> PhantomData<T>`[src]

`impl Default for AtomicBool`[src][−]

`pub fn default() -> AtomicBool`[src][−]

`impl Default for SipHasher`[src][−]

`pub fn default() -> SipHasher`[src]

`impl<T> Default for Wrapping<T> where T: Default,` [src][−]

`pub fn default() -> Wrapping<T>`[src]

`impl Default for AtomicI8`[src][−]

`pub fn default() -> AtomicI8`[src]

`impl<T> Default for Lazy<T, fn() -> T> where T: Default,` [src][−]

`pub fn default() -> Lazy<T, fn() -> T>`[src][−]

`impl<T> Default for UnsafeCell<T> where T: Default,` [src][−]

`pub fn default() -> UnsafeCell<T>`[src][−]

`impl<T> Default for OnceCell<T>`[src][−]

`pub fn default() -> OnceCell<T>`[src]

`impl Default for AtomicU16`[src][−]

`pub fn default() -> AtomicU16`[src]

`impl Default for AtomicU64`[src][−]

`pub fn default() -> AtomicU64`[src]

`impl Default for Duration`[src][−]

`pub fn default() -> Duration`[src]

`impl Default for AtomicU32`[src][−]

`pub fn default() -> AtomicU32`[src]

`impl Default for AtomicUsize`[src][−]

`pub fn default() -> AtomicUsize`[src]

`impl Default for AtomicI32`[src][−]

`pub fn default() -> AtomicI32`[src]

`impl<T> Default for RefCell<T> where T: Default,` [src][−]

`pub fn default() -> RefCell<T>`[src][−]

`impl Default for AtomicU8`[src][−]

`pub fn default() -> AtomicU8`[src]

`impl Default for PhantomPinned`[src][−]

`pub fn default() -> PhantomPinned`[src]

`impl<T> Default for Cell<T> where T: Default,` [src][−]

`pub fn default() -> Cell<T>`[src][−]

`impl Default for AtomicIsize`[src][−]

`pub fn default() -> AtomicIsize`[src]

`impl Default for AtomicI64`[src][−]

`pub fn default() -> AtomicI64`[src]

`impl<H> Default for BuildHasherDefault<H>`[src][−]

`pub fn default() -> BuildHasherDefault<H>`[src]

`impl<T> Default for AtomicPtr<T>`[src][−]

`pub fn default() -> AtomicPtr<T>`[src][−]

`impl Default for AtomicI16`[src][−]

`pub fn default() -> AtomicI16`[src]

`impl Default for ()`[src][+]

`pub fn default()`[src][−]

`impl Default for Error`[src][+]

`pub fn default() -> Error`[src]

`impl Default for RangeFull`[src][+]

`pub fn default() -> RangeFull`[src]

`impl Default for bool`[src][+]

`pub fn default() -> bool`[src][−]

`impl Default for char`[src][+]

`pub fn default() -> char`[src][−]

`impl Default for f32`[src][+]

`pub fn default() -> f32`[src][−]

`impl Default for f64`[src][+]

`pub fn default() -> f64`[src][−]

`impl Default for i8`[src][+]

`pub fn default() -> i8`[src][−]

`impl Default for i16`[src][+]

`pub fn default() -> i16`[src][−]

`impl Default for i32`[src][+]

`pub fn default() -> i32`[src][−]

`impl Default for i64`[src][+]

`pub fn default() -> i64`[src][−]

`impl Default for i128`[src][+]

`pub fn default() -> i128`[src][−]

`impl Default for isize`[src][+]

`pub fn default() -> isize`[src][−]

`impl Default for u8`[src][+]

`pub fn default() -> u8`[src][−]

`impl Default for u16`[src][+]

`pub fn default() -> u16`[src][−]

`impl Default for u32`[src][+]