core::lazy::Lazy - Rust
Description: API documentation for the Rust `Lazy` struct in crate `core`.
Keywords: rust, rustlang, rust-lang, Lazy

# [−][src]Struct core::lazy::Lazy

    pub struct Lazy<T, F = fn() -> T> { /* fields omitted */ }

🔬 This is a nightly-only experimental API. (`once_cell` #74465)

A value which is initialized on the first access.

# Examples

    #![feature(once_cell)]

    use std::lazy::Lazy;

    let lazy: Lazy<i32> = Lazy::new(|| {
        println!("initializing");
        92
    });
    println!("ready");
    println!("{}", *lazy);
    println!("{}", *lazy);

    // Prints:
    //   ready
    //   initializing
    //   92
    //   92

Run

## Implementations

### `impl<T, F> Lazy<T, F>`[src]

#### `pub const fn new(init: F) -> Lazy<T, F>`[src]

🔬 This is a nightly-only experimental API. (`once_cell` #74465)

Creates a new lazy value with the given initializing function.

# Examples

    #![feature(once_cell)]

    use std::lazy::Lazy;

    let hello = "Hello, World!".to_string();

    let lazy = Lazy::new(|| hello.to_uppercase());

    assert_eq!(&*lazy, "HELLO, WORLD!");

Run

### `impl<T, F: FnOnce() -> T> Lazy<T, F>`[src]

#### `pub fn force(this: &Lazy<T, F>) -> &T`[src]

🔬 This is a nightly-only experimental API. (`once_cell` #74465)

Forces the evaluation of this lazy value and returns a reference to the result.

This is equivalent to the `Deref` impl, but is explicit.

# Examples

    #![feature(once_cell)]

    use std::lazy::Lazy;

    let lazy = Lazy::new(|| 92);

    assert_eq!(Lazy::force(&lazy), &92);
    assert_eq!(&*lazy, &92);

Run

## Trait Implementations

### `impl<T: Debug, F> Debug for Lazy<T, F>`[src]

#### `fn fmt(&self, f: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

### `impl<T: Default> Default for Lazy<T>`[src]

#### `fn default() -> Lazy<T>`[src]

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

### `impl<T, F: FnOnce() -> T> Deref for Lazy<T, F>`[src]

#### `type Target = T`

The resulting type after dereferencing.

#### `fn deref(&self) -> &T`[src]

Dereferences the value.

## Auto Trait Implementations

### `impl<T, F> Send for Lazy<T, F> where
F: Send,
T: Send,` [src]

### `impl<T, F = fn() -> T> !Sync for Lazy<T, F>`[src]

### `impl<T, F> Unpin for Lazy<T, F> where
F: Unpin,
T: Unpin,` [src]

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&Self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&Self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut Self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T`[src]

#### `pub fn from(T) -> T`[src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `pub fn into(Self) -> U`[src]

Performs the conversion.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `pub fn try_into(Self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.