# Struct std::cell::RefMut [−] [src]

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

A wrapper type for a mutably borrowed value from a `RefCell<T>`.

See the module-level documentation for more.

## Methods

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

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

Unstable (`cell_extras` #27746)

: recently added

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

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

This is an associated function that needs to be used as `RefMut::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, RefMut}; let c = RefCell::new((5, 'b')); { let b1: RefMut<(u32, char)> = c.borrow_mut(); let mut b2: RefMut<u32> = RefMut::map(b1, |t| &mut t.0); assert_eq!(*b2, 5); *b2 = 42; } assert_eq!(*c.borrow(), (42, 'b')); }

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

    let c = RefCell::new((5, 'b'));
    {
        let b1: RefMut<(u32, char)> = c.borrow_mut();
        let mut b2: RefMut<u32> = RefMut::map(b1, |t| &mut t.0);
        assert_eq!(*b2, 5);
        *b2 = 42;
    }
    assert_eq!(*c.borrow(), (42, 'b'));

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

Unstable (`cell_extras` #27746)

: recently added

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

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

This is an associated function that needs to be used as `RefMut::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, RefMut}; let c = RefCell::new(Ok(5)); { let b1: RefMut<Result<u32, ()>> = c.borrow_mut(); let mut b2: RefMut<u32> = RefMut::filter_map(b1, |o| { o.as_mut().ok() }).unwrap(); assert_eq!(*b2, 5); *b2 = 42; } assert_eq!(*c.borrow(), Ok(42)); }

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

    let c = RefCell::new(Ok(5));
    {
        let b1: RefMut<Result<u32, ()>> = c.borrow_mut();
        let mut b2: RefMut<u32> = RefMut::filter_map(b1, |o| {
            o.as_mut().ok()
        }).unwrap();
        assert_eq!(*b2, 5);
        *b2 = 42;
    }
    assert_eq!(*c.borrow(), Ok(42));

## Trait Implementations

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

#### `type Target = T`

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

### `impl<'b, T> DerefMut for RefMut<'b, T> where T: ?Sized`

#### `fn deref_mut(&mut self) -> &mut T`

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

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

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