Struct core::cell::RefMut

pub struct RefMut<'b, T: ?Sized + 'b> { /* private fields */ }

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

See the module-level documentation for more.

Implementations

impl<'b, T: ?Sized> RefMut<'b, T>

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

Makes 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.

Examples

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'));

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

🔬 This is a nightly-only experimental API. (cell_filter_map #81061)

Makes a new RefMut for an optional component of the borrowed data. The original guard is returned as an Err(..) if the closure returns None.

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.

Examples

#![feature(cell_filter_map)]

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

let c = RefCell::new(vec![1, 2, 3]);

{
    let b1: RefMut<Vec<u32>> = c.borrow_mut();
    let mut b2: Result<RefMut<u32>, _> = RefMut::filter_map(b1, |v| v.get_mut(1));

    if let Ok(mut b2) = b2 {
        *b2 += 2;
    }
}

assert_eq!(*c.borrow(), vec![1, 4, 3]);

pub fn map_split<U: ?Sized, V: ?Sized, F>(
    orig: RefMut<'b, T>,
    f: F
) -> (RefMut<'b, U>, RefMut<'b, V>) where
    F: FnOnce(&mut T) -> (&mut U, &mut V), 

Splits a RefMut into multiple RefMuts for different components of the borrowed data.

The underlying RefCell will remain mutably borrowed until both returned RefMuts go out of scope.

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

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

Examples

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

let cell = RefCell::new([1, 2, 3, 4]);
let borrow = cell.borrow_mut();
let (mut begin, mut end) = RefMut::map_split(borrow, |slice| slice.split_at_mut(2));
assert_eq!(*begin, [1, 2]);
assert_eq!(*end, [3, 4]);
begin.copy_from_slice(&[4, 3]);
end.copy_from_slice(&[2, 1]);

pub fn leak(orig: RefMut<'b, T>) -> &'b mut T

🔬 This is a nightly-only experimental API. (cell_leak #69099)

Convert into a mutable reference to the underlying data.

The underlying RefCell can not be borrowed from again and will always appear already mutably borrowed, making the returned reference the only to the interior.

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

Examples

#![feature(cell_leak)]
use std::cell::{RefCell, RefMut};
let cell = RefCell::new(0);

let value = RefMut::leak(cell.borrow_mut());
assert_eq!(*value, 0);
*value = 1;

assert!(cell.try_borrow_mut().is_err());

Trait Implementations

impl<T: ?Sized + Debug> Debug for RefMut<'_, T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: ?Sized> Deref for RefMut<'_, T>

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<T: ?Sized> DerefMut for RefMut<'_, T>

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

Mutably dereferences the value.

impl<T: ?Sized + Display> Display for RefMut<'_, T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'b, T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<RefMut<'b, U>> for RefMut<'b, T>