Trait nom::lib::std::prelude::v1::rust_2018::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 }
}

Implementations on Foreign Types

`impl Default for CString`[src]

`pub fn default() -> CString`[src][−]

Creates an empty CString.

`impl<T> Default for Mutex<T> where T: Default + ?Sized,` [src]

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

Creates a Mutex<T>, with the Default value for T.

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

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

Creates a new RwLock<T>, with the Default value for T.

`impl Default for Condvar`[src]

`pub fn default() -> Condvar`[src][−]

Creates a Condvar which is ready to be waited on and notified.

Trait nom::lib::std::prelude::v1::rust_2018::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 Default for CString[src]

pub fn default() -> CString[src][−]

impl<T> Default for Mutex<T> where T: Default + ?Sized, [src]

pub fn default() -> Mutex<T>[src][−]

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

pub fn default() -> RwLock<T>[src][−]

impl Default for Condvar[src]

pub fn default() -> Condvar[src][−]

impl<'_> Default for &'_ CStr[src]

pub fn default() -> &'_ CStr[src]

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

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

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

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

impl Default for PathBuf[src]

pub fn default() -> PathBuf[src]

impl Default for OsString[src]

pub fn default() -> OsString[src][−]

impl<T> Default for SyncOnceCell<T>[src]

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

impl<'_> Default for &'_ OsStr[src]

pub fn default() -> &'_ OsStr[src][−]

impl Default for i32[src]

pub fn default() -> i32[src][−]

impl<T> Default for [T; 15] where T: Default, [src]

pub fn default() -> [T; 15][src]

impl Default for u16[src]

pub fn default() -> u16[src][−]

impl Default for char[src]

pub fn default() -> char[src][−]

impl<'_> Default for &'_ mut str[src]

pub fn default() -> &'_ mut str[src][−]

impl<T> Default for [T; 1] where T: Default, [src]

pub fn default() -> [T; 1][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 [T; 22] where T: Default, [src]

pub fn default() -> [T; 22][src]

impl<T> Default for [T; 25] where T: Default, [src]

pub fn default() -> [T; 25][src]

impl Default for AtomicUsize[src]

pub fn default() -> AtomicUsize[src]

impl<A, B, C> Default for (A, B, C) where C: Default, A: Default, B: Default, [src]

pub fn default() -> (A, B, C)[src]

impl<T> Default for [T; 31] where T: Default, [src]

pub fn default() -> [T; 31][src]

impl<A, B, C, D> Default for (A, B, C, D) where C: Default, A: Default, B: Default, D: Default, [src]

pub fn default() -> (A, B, C, D)[src]

impl Default for bool[src]

pub fn default() -> bool[src][−]

impl<T> Default for [T; 26] where T: Default, [src]

pub fn default() -> [T; 26][src]

impl<T> Default for [T; 18] where T: Default, [src]

pub fn default() -> [T; 18][src]

impl<T> Default for [T; 20] where T: Default, [src]

pub fn default() -> [T; 20][src]

impl<A> Default for (A,) where A: Default, [src]

pub fn default() -> (A,)[src]

impl Default for ()[src]

pub fn default()[src][−]

impl<'_> Default for &'_ str[src]

pub fn default() -> &'_ str[src][−]

impl<A, B, C, D, E, F, G> Default for (A, B, C, D, E, F, G) where C: Default, F: Default, E: Default, G: Default, A: Default, B: Default, D: Default, [src]

pub fn default() -> (A, B, C, D, E, F, G)[src]

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

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

impl<T> Default for [T; 17] where T: Default, [src]

pub fn default() -> [T; 17][src]

impl<T> Default for [T; 14] where T: Default, [src]

pub fn default() -> [T; 14][src]

impl<A, B, C, D, E, F, G, H, I, J, K> Default for (A, B, C, D, E, F, G, H, I, J, K) where C: Default, F: Default, E: Default, I: Default, G: Default, H: Default, A: Default, B: Default, D: Default, J: Default, K: Default, [src]

pub fn default() -> (A, B, C, D, E, F, G, H, I, J, K)[src]

Trait nom::lib::std::prelude::v1::rust_2018::Default1.0.0[−][src]

How can I implement `Default`?

`pub fn default() -> Self`[src][−]

`impl Default for CString`[src]

`pub fn default() -> CString`[src][−]

`impl<T> Default for Mutex<T> where T: Default + ?Sized,` [src]

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

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

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

`impl Default for Condvar`[src]

`pub fn default() -> Condvar`[src][−]

`impl<'_> Default for &'_ CStr`[src]

`pub fn default() -> &'_ CStr`[src]

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

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

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

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

`impl Default for PathBuf`[src]

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

`impl Default for OsString`[src]

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

`impl<T> Default for SyncOnceCell<T>`[src]

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

`impl<'_> Default for &'_ OsStr`[src]

`pub fn default() -> &'_ OsStr`[src][−]

`impl Default for i32`[src]

`pub fn default() -> i32`[src][−]

`impl<T> Default for [T; 15] where T: Default,` [src]

`pub fn default() -> [T; 15]`[src]

`impl Default for u16`[src]

`pub fn default() -> u16`[src][−]

`impl Default for char`[src]

`pub fn default() -> char`[src][−]

`impl<'_> Default for &'_ mut str`[src]

`pub fn default() -> &'_ mut str`[src][−]

`impl<T> Default for [T; 1] where T: Default,` [src]

`pub fn default() -> [T; 1]`[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 [T; 22] where T: Default,` [src]

`pub fn default() -> [T; 22]`[src]

`impl<T> Default for [T; 25] where T: Default,` [src]

`pub fn default() -> [T; 25]`[src]

`impl Default for AtomicUsize`[src]

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

`impl<A, B, C> Default for (A, B, C) where C: Default, A: Default, B: Default,` [src]

`pub fn default() -> (A, B, C)`[src]

`impl<T> Default for [T; 31] where T: Default,` [src]

`pub fn default() -> [T; 31]`[src]

`impl<A, B, C, D> Default for (A, B, C, D) where C: Default, A: Default, B: Default, D: Default,` [src]

`pub fn default() -> (A, B, C, D)`[src]

`impl Default for bool`[src]

`pub fn default() -> bool`[src][−]

`impl<T> Default for [T; 26] where T: Default,` [src]

`pub fn default() -> [T; 26]`[src]

`impl<T> Default for [T; 18] where T: Default,` [src]

`pub fn default() -> [T; 18]`[src]

`impl<T> Default for [T; 20] where T: Default,` [src]

`pub fn default() -> [T; 20]`[src]

`impl<A> Default for (A,) where A: Default,` [src]

`pub fn default() -> (A,)`[src]

`impl Default for ()`[src]

`pub fn default()`[src][−]

`impl<'_> Default for &'_ str`[src]

`pub fn default() -> &'_ str`[src][−]

`impl<A, B, C, D, E, F, G> Default for (A, B, C, D, E, F, G) where C: Default, F: Default, E: Default, G: Default, A: Default, B: Default, D: Default,` [src]

`pub fn default() -> (A, B, C, D, E, F, G)`[src]

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

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

`impl<T> Default for [T; 17] where T: Default,` [src]

`pub fn default() -> [T; 17]`[src]

`impl<T> Default for [T; 14] where T: Default,` [src]

`pub fn default() -> [T; 14]`[src]

`impl<A, B, C, D, E, F, G, H, I, J, K> Default for (A, B, C, D, E, F, G, H, I, J, K) where C: Default, F: Default, E: Default, I: Default, G: Default, H: Default, A: Default, B: Default, D: Default, J: Default, K: Default,` [src]

`pub fn default() -> (A, B, C, D, E, F, G, H, I, J, K)`[src]

`impl<A, B, C, D, E, F, G, H, I, J, K, L> Default for (A, B, C, D, E, F, G, H, I, J, K, L) where C: Default, F: Default, E: Default, I: Default, G: Default, H: Default, A: Default, B: Default, D: Default, J: Default, K: Default, L: Default,` [src]

`pub fn default() -> (A, B, C, D, E, F, G, H, I, J, K, L)`[src]

`impl<T> Default for [T; 16] where T: Default,` [src]

`pub fn default() -> [T; 16]`[src]

`impl Default for f64`[src]