Trait otter_api_tests::imports::failure::_core::default::Default1.0.0[−][src]

pub trait Default {
    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.

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

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

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

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

Creates an empty CString.

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

Creates a new lazy value using Default as the initializing function.

Constructs an empty OsString.

Returns the default value of 0.0

Creates an empty mutable str

Returns the default value of 0.0

Returns the default value of 0

Returns the default value of 0

Returns the default value of \x00

Creates a mutable empty slice.

Returns the default value of 0

Returns the default value of 0

Returns the default value of 0

Returns the default value of 0

Returns the default value of false

Returns the default value of 0

Returns the default value of 0

Returns the default value of 0

Returns the default value of 0

Returns the default value of 0

Returns the default value of ()

Creates an empty str

Returns the default value of 0

Creates an empty slice.

Creates an empty LinkedList<T>.

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

Examples

use std::rc::Rc;

let x: Rc<i32> = Default::default();
assert_eq!(*x, 0);

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

Creates an empty String.

Constructs a new Weak<T>, without allocating any memory. Calling upgrade on the return value always gives None.

Examples

use std::rc::Weak;

let empty: Weak<i64> = Default::default();
assert!(empty.upgrade().is_none());

Creates an empty Vec<T>.

Constructs a new Weak<T>, without allocating memory. Calling upgrade on the return value always gives None.

Examples

use std::sync::Weak;

let empty: Weak<i64> = Default::default();
assert!(empty.upgrade().is_none());

Creates an empty BinaryHeap<T>.

The default match kind is MatchKind::Standard.

Create a new tinfl_decompressor with all fields set to 0.

Initialize the compressor with a level of 4, zlib wrapper and the default strategy.

Choose the default compression, a balance between speed and size.

The defaults are that of https://url.spec.whatwg.org/#idna

Returns a pixel density with a pixel aspect ratio of 1

Returns the options describing the default compression level.

Initialize the compressor with a level of 4, zlib wrapper and the default strategy.

Create a new tinfl_decompressor with all fields set to 0.

Creates an empty iterator.

Creates an empty iterator.

Returns a style with no properties set. Formatting text using this style returns the exact same text.

use ansi_term::Style;
assert_eq!(None,  Style::default().foreground);
assert_eq!(None,  Style::default().background);
assert_eq!(false, Style::default().is_bold);
assert_eq!("txt", Style::default().paint("txt").to_string());

Returns a Uri representing /

Create an empty Full.

impl Default for Body

Returns Body::empty().

Returns the current default dispatcher

Return an empty IndexMap

Return an empty IndexSet

Creates an empty HashMap<K, V, S>, with the Default value for the hasher.

Creates an empty HashSet<T, S> with the Default value for the hasher.

Implementors

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);

The default timestamp precision is seconds.

Creates a new DefaultHasher using new. See its documentation for more.

Constructs a new RandomState.

Constructs an ‘default’ datetime of 1980-01-01 00:00:00

Creates an AtomicBool initialized to false.

Creates an empty OsStr.

Creates an owned Cow<’a, B> with the default value for the contained owned value.

Creates an empty BTreeMap.

Creates an empty HashMap<K, V, S>, with the Default value for the hasher.

Returns None.

Examples

let opt: Option<u32> = Option::default();
assert!(opt.is_none());

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

Examples

use std::sync::Arc;

let x: Arc<i32> = Default::default();
assert_eq!(*x, 0);

Creates an empty BTreeSet.

Creates an empty VecDeque<T>.

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

Creates a new lazy value using Default as the initializing function.

Creates a new lazy value using Default as the initializing function.

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

Creates an UnsafeCell, with the Default value for T.

Creates a new lazy value using Default as the initializing function.

Creates a null AtomicPtr<T>.

Creates an empty HashSet<T, S> with the Default value for the hasher.

Return an empty array

Return an empty ArrayString