impl<'b, T: ?Sized> RefMut<'b, T>

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'));

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>,

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

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]);

fn try_map<U: ?Sized, E>(orig: RefMut<'b, T>, f: impl FnOnce(&mut T) -> Result<&mut U, E>) -> Result<RefMut<'b, U>, (Self, E)>

Tries to makes a new RefMut for a component of the borrowed data. On failure, the original guard is returned alongside with the error returned by the closure.

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

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

Examples

#![feature(refcell_try_map)]
use std::cell::{RefCell, RefMut};
use std::str::{from_utf8_mut, Utf8Error};

let c = RefCell::new(vec![0x68, 0x65, 0x6C, 0x6C, 0x6F]);
{
    let b1: RefMut<'_, Vec<u8>> = c.borrow_mut();
    let b2: Result<RefMut<'_, str>, _> = RefMut::try_map(b1, |v| from_utf8_mut(v));
    let mut b2 = b2.unwrap();
    assert_eq!(&*b2, "hello");
    b2.make_ascii_uppercase();
}
assert_eq!(*c.borrow(), "HELLO".as_bytes());

let c = RefCell::new(vec![0xFF]);
let b1: RefMut<'_, Vec<u8>> = c.borrow_mut();
let b2: Result<_, (RefMut<'_, Vec<u8>>, Utf8Error)> = RefMut::try_map(b1, |v| from_utf8_mut(v));
let (b3, e) = b2.unwrap_err();
assert_eq!(*b3, vec![0xFF]);
assert_eq!(e.valid_up_to(), 0);

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]);

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

Converts 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());