# tokio::sync::RwLockReadGuard - Rust
API documentation for the Rust `RwLockReadGuard` struct in crate `tokio`.
Keywords: rust, rustlang, rust-lang, RwLockReadGuard

# Struct tokio::sync::RwLockReadGuard [−] [src]

    pub struct RwLockReadGuard<'a, T: ?Sized> { /* fields omitted */ }

RAII structure used to release the shared read access of a lock when dropped.

This structure is created by the `read` method on `RwLock`.

## Implementations

### `impl<'a, T> RwLockReadGuard<'a, T>` [src]

#### `pub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, U> where
F: FnOnce(&T) -> &U,` [src]

Make a new `RwLockReadGuard` for a component of the locked data.

This operation cannot fail as the `RwLockReadGuard` passed in already locked the data.

This is an associated function that needs to be used as `RwLockReadGuard::map(...)`. A method would interfere with methods of the same name on the contents of the locked data.

This is an asynchronous version of `RwLockReadGuard::map` from the `parking_lot` crate.

# Examples

    use tokio::sync::{RwLock, RwLockReadGuard};

    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    struct Foo(u32);

    let lock = RwLock::new(Foo(1));

    let guard = lock.read().await;
    let guard = RwLockReadGuard::map(guard, |f| &f.0);

    assert_eq!(1, *guard);

#### `pub fn try_map<F, U: ?Sized>(
this: Self,
f: F
) -> Result<RwLockReadGuard<'a, U>, Self> where
F: FnOnce(&T) -> Option<&U>,` [src]

Attempts to make a new `RwLockReadGuard` for a component of the locked data. The original guard is returned if the closure returns `None`.

This operation cannot fail as the `RwLockReadGuard` passed in already locked the data.

This is an associated function that needs to be used as `RwLockReadGuard::try_map(..)`. A method would interfere with methods of the same name on the contents of the locked data.

This is an asynchronous version of `RwLockReadGuard::try_map` from the `parking_lot` crate.

# Examples

    use tokio::sync::{RwLock, RwLockReadGuard};

    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
    struct Foo(u32);

    let lock = RwLock::new(Foo(1));

    let guard = lock.read().await;
    let guard = RwLockReadGuard::try_map(guard, |f| Some(&f.0)).expect("should not fail");

    assert_eq!(1, *guard);

## Trait Implementations

### `impl<'a, T: ?Sized> Debug for RwLockReadGuard<'a, T> where
T: Debug,` [src]

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

Formats the value using the given formatter. Read more

### `impl<T: ?Sized> Deref for RwLockReadGuard<'_, T>` [src]

#### `type Target = T`

The resulting type after dereferencing.

#### `fn deref(&self) -> &Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;`
` [src]

Dereferences the value.

### `impl<'a, T: ?Sized> Display for RwLockReadGuard<'a, T> where
T: Display,` [src]

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

Formats the value using the given formatter. Read more

### `impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T>` [src]

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

Executes the destructor for this type. Read more

### `impl<T: ?Sized> Send for RwLockReadGuard<'_, T> where
T: Sync,` [src]

### `impl<T: ?Sized> Sync for RwLockReadGuard<'_, T> where
T: Send + Sync,` [src]

## Auto Trait Implementations

### `impl<'a, T> !RefUnwindSafe for RwLockReadGuard<'a, T>` [src]

### `impl<'a, T: ?Sized> Unpin for RwLockReadGuard<'a, T>` [src]

### `impl<'a, T> !UnwindSafe for RwLockReadGuard<'a, T>` [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ⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;`
` [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ⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;`
` [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> ToString for T where
T: Display + ?Sized,` [src]

#### `pub default fn to_string(&self) -> String` [src]

Converts the given value to a `String`. Read more

### `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.