Struct std::cell::RefMut

1.0.0 · source · [−]
pub struct RefMut<'b, T> where
    T: 'b + ?Sized, { /* private fields */ }
Expand description

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

See the module-level documentation for more.

Implementations

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'));
Run

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]);
Run

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]);
Run
🔬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());
Run

Trait Implementations

Formats the value using the given formatter. Read more

The resulting type after dereferencing.

Dereferences the value.

Mutably dereferences the value.

Formats the value using the given formatter. Read more

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

Converts the given value to a String. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.