pub struct RefMut<'a, T: ?Sized + 'a> { /* private fields */ }
Expand description
A mutable reference to data in a TrustCell
.
Access the value via std::ops::DerefMut
(e.g. *val
)
Implementations
sourceimpl<'a, T: ?Sized> RefMut<'a, T>
impl<'a, T: ?Sized> RefMut<'a, T>
sourcepub fn map<U, F>(self, f: F) -> RefMut<'a, U> where
F: FnOnce(&mut T) -> &mut U,
U: ?Sized,
pub fn map<U, F>(self, f: F) -> RefMut<'a, U> where
F: FnOnce(&mut T) -> &mut U,
U: ?Sized,
Makes a new RefMut
for a component of the borrowed data which
preserves the existing borrow.
The TrustCell
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 RefMut
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 TrustCell
.
use shred::cell::{RefMut, TrustCell};
let cb = TrustCell::new(Box::new(5));
// Borrowing the cell causes the `RefMut` 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: RefMut<'_, 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 `RefMut` store a reference directly to the value on the heap.
let pure_ref: RefMut<'_, usize> = RefMut::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 = TrustCell::new((5, 'b'));
let b1: RefMut<'_, (u32, char)> = c.borrow_mut();
let b2: RefMut<'_, u32> = RefMut::map(b1, |t| &mut t.0);
assert_eq!(*b2, 5);
Trait Implementations
Auto Trait Implementations
impl<'a, T: ?Sized> RefUnwindSafe for RefMut<'a, T> where
T: RefUnwindSafe,
impl<'a, T: ?Sized> Send for RefMut<'a, T> where
T: Send,
impl<'a, T: ?Sized> Sync for RefMut<'a, T> where
T: Sync,
impl<'a, T: ?Sized> Unpin for RefMut<'a, T>
impl<'a, T> !UnwindSafe for RefMut<'a, T>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more