# Struct std::cell::Ref 1.0.0 [−] [src]

    pub struct Ref<'b, T> where T: 'b + ?Sized {
        // some fields omitted
    }

Wraps a borrowed reference to a value in a `RefCell` box. A wrapper type for an immutably borrowed value from a `RefCell<T>`.

See the module-level documentation for more.

## Methods

### `impl<'b, T> Ref<'b, T> where T: ?Sized`

#### `fn clone(orig: &Ref<'b, T>) -> Ref<'b, T>`

Unstable (`cell_extras` #27746)

: likely to be moved to a method, pending language changes

Copies a `Ref`.

The `RefCell` is already immutably borrowed, so this cannot fail.

This is an associated function that needs to be used as `Ref::clone(...)`. A `Clone` implementation or a method would interfere with the widespread use of `r.borrow().clone()` to clone the contents of a `RefCell`.

#### `fn map<U, F>(orig: Ref<'b, T>, f: F) -> Ref<'b, U> where F: FnOnce(&T) -> &U, U: ?Sized`
1.8.0

Make a new `Ref` for a component of the borrowed data.

The `RefCell` is already immutably borrowed, so this cannot fail.

This is an associated function that needs to be used as `Ref::map(...)`. A method would interfere with methods of the same name on the contents of a `RefCell` used through `Deref`.

# Example

fn main() { use std::cell::{RefCell, Ref}; let c = RefCell::new((5, 'b')); let b1: Ref<(u32, char)> = c.borrow(); let b2: Ref<u32> = Ref::map(b1, |t| &t.0); assert_eq!(*b2, 5) }

    use std::cell::{RefCell, Ref};

    let c = RefCell::new((5, 'b'));
    let b1: Ref<(u32, char)> = c.borrow();
    let b2: Ref<u32> = Ref::map(b1, |t| &t.0);
    assert_eq!(*b2, 5)

#### `fn filter_map<U, F>(orig: Ref<'b, T>, f: F) -> Option<Ref<'b, U>> where F: FnOnce(&T) -> Option<&U>, U: ?Sized`

Deprecated since 1.8.0

: can be built on `Ref::map`: https://crates.io/crates/ref_filter_map

Unstable (`cell_extras` #27746)

: can be built on `Ref::map`: https://crates.io/crates/ref_filter_map

Make a new `Ref` for an optional component of the borrowed data, e.g. an enum variant.

The `RefCell` is already immutably borrowed, so this cannot fail.

This is an associated function that needs to be used as `Ref::filter_map(...)`. A method would interfere with methods of the same name on the contents of a `RefCell` used through `Deref`.

# Example

#![feature(cell_extras)] fn main() { use std::cell::{RefCell, Ref}; let c = RefCell::new(Ok(5)); let b1: Ref<Result<u32, ()>> = c.borrow(); let b2: Ref<u32> = Ref::filter_map(b1, |o| o.as_ref().ok()).unwrap(); assert_eq!(*b2, 5) }

    use std::cell::{RefCell, Ref};

    let c = RefCell::new(Ok(5));
    let b1: Ref<Result<u32, ()>> = c.borrow();
    let b2: Ref<u32> = Ref::filter_map(b1, |o| o.as_ref().ok()).unwrap();
    assert_eq!(*b2, 5)

## Trait Implementations

### `impl<'b, T> Deref for Ref<'b, T> where T: ?Sized`

#### `type Target = T`

#### `fn deref(&self) -> &T`

### `impl<'b, T, U> CoerceUnsized<Ref<'b, U>> for Ref<'b, T> where T: Unsize<U> + ?Sized, U: ?Sized`

### `impl<'b, T> Debug for Ref<'b, T> where T: Debug + ?Sized`

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`

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