Struct rt_ref::CellRefMut

pub struct CellRefMut<'a, T>
where
    T: ?Sized + 'a,
{ /* private fields */ }

A mutable reference to data in a Cell.

Access the value via std::ops::DerefMut (e.g. *val)

Implementations

impl<'a, T> CellRefMut<'a, T>

where T: ?Sized,

pub fn map<U, F>(self, f: F) -> CellRefMut<'a, U>

where F: FnOnce(&mut T) -> &mut U, U: ?Sized,

Makes a new CellRefMut for a component of the borrowed data which preserves the existing borrow.

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

This is an associated function that needs to be used as CellRefMut::map(..). A method would interfere with methods of the same name on the contents of a CellRefMut used through DerefMut. Further this preserves the borrow of the value and hence does the proper cleanup when it’s dropped.

Examples

This can also be used to avoid pointer indirection when a boxed item is stored in the Cell.

use rt_ref::{Cell, CellRefMut};

let cb = Cell::new(Box::new(5));

// Borrowing the cell causes the `CellRefMut` to store a reference to the `Box`, which is a
// pointer to the value on the heap, and not a reference directly to the value.
let boxed_ref: CellRefMut<'_, Box<usize>> = cb.borrow_mut();
assert_eq!(**boxed_ref, 5); // Notice the double deref to get the actual value.

// By using `map` we can let `CellRefMut` store a reference directly to the value on the heap.
let pure_ref: CellRefMut<'_, usize> = CellRefMut::map(boxed_ref, Box::as_mut);

assert_eq!(*pure_ref, 5);

We can also use map to get a reference to a sub-part of the borrowed value.

let c = Cell::new((5, 'b'));

let b1: CellRefMut<'_, (u32, char)> = c.borrow_mut();
let b2: CellRefMut<'_, u32> = CellRefMut::map(b1, |t| &mut t.0);
assert_eq!(*b2, 5);

Trait Implementations

impl<'a, T> Debug for CellRefMut<'a, T>

where T: ?Sized + 'a + Debug,

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

Formats the value using the given formatter.

impl<'a, T> Deref for CellRefMut<'a, T>

where T: ?Sized,

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

Dereferences the value.

impl<'a, T> DerefMut for CellRefMut<'a, T>

where T: ?Sized,

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

Mutably dereferences the value.

impl<'a, T> Drop for CellRefMut<'a, T>

where T: ?Sized,

fn drop(&mut self)

Executes the destructor for this type.