RefMut in core::cell - Rust (original) (raw)

Struct RefMut

1.6.0 · Source

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

Expand description

Source§

1.8.0 · Source

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 asRefMut::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'));

1.63.0 · Source

Makes a new RefMut for an optional component of the borrowed data. The original guard is returned as an Err(..) if the closure returnsNone.

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

This is an associated function that needs to be used asRefMut::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]);

Source

🔬This is a nightly-only experimental API. (refcell_try_map #143801)

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 asRefMut::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);

1.35.0 · Source

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 asRefMut::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]);

Source

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

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 asRefMut::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());