# once_cell::race::OnceBox - Rust
API documentation for the Rust `OnceBox` struct in crate `once_cell`.
Keywords: rust, rustlang, rust-lang, OnceBox

# Struct once_cell::race::OnceBox [−] [src]

    pub struct OnceBox<T> { /* fields omitted */ }

A thread-safe cell which can be written to only once.

## Implementations

### `impl<T> OnceBox<T>` [src]

#### `pub const fn new() -> OnceBox<T>` [src]

Creates a new empty cell.

#### `pub fn get(&self) -> Option<&T>` [src]

Gets a reference to the underlying value.

#### `pub fn set(&self, value: Box<T>) -> Result<(), Box<T>>` [src]

Sets the contents of this cell to `value`.

Returns `Ok(())` if the cell was empty and `Err(value)` if it was full.

#### `pub fn get_or_init<F>(&self, f: F) -> &T where
F: FnOnce() -> Box<T>,` [src]

Gets the contents of the cell, initializing it with `f` if the cell was empty.

If several threads concurrently run `get_or_init`, more than one `f` can be called. However, all threads will return the same value, produced by some `f`.

#### `pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E> where
F: FnOnce() -> Result<Box<T>, E>,` [src]

Gets the contents of the cell, initializing it with `f` if the cell was empty. If the cell was empty and `f` failed, an error is returned.

If several threads concurrently run `get_or_init`, more than one `f` can be called. However, all threads will return the same value, produced by some `f`.

## Trait Implementations

### `impl<T: Debug> Debug for OnceBox<T>` [src]

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

Formats the value using the given formatter. Read more

### `impl<T> Default for OnceBox<T>` [src]

#### `fn default() -> Self` [src]

Returns the "default value" for a type. Read more

### `impl<T> Drop for OnceBox<T>` [src]

#### `fn drop(&mut self)` [src]

Executes the destructor for this type. Read more

### `impl<T: Sync + Send> Sync for OnceBox<T>` [src]

## Auto Trait Implementations

### `impl<T> RefUnwindSafe for OnceBox<T> where
T: RefUnwindSafe,` [src]

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

### `impl<T> Unpin for OnceBox<T>` [src]

### `impl<T> UnwindSafe for OnceBox<T> where
T: RefUnwindSafe + UnwindSafe,` [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) -> 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(value: 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.