Struct ThinCell 

pub struct ThinCell<T: ?Sized> { /* private fields */ }

A compact (1-usize), single-threaded smart pointer combining Rc and borrow_mut-only RefCell

Implementations

impl<T> ThinCell<T>

pub fn new(data: T) -> Self

Creates a new ThinCell wrapping the given data.

pub fn try_unwrap(self) -> Result<T, Self>

Consumes the ThinCell, returning the inner value if there are no other owners and it is not currently borrowed.

pub unsafe fn unwrap_unchecked(self) -> T

Consumes the ThinCell, returning the inner value.

Safety

The caller must guarantee that there are no other owners and it is not currently borrowed.

impl<T: ?Sized> ThinCell<T>

pub unsafe fn new_unsize<U>( data: U, coerce: impl Fn(*const Inner<U>) -> *const Inner<T>, ) -> Self

Creates a new ThinCell<U> from data: U and coerces it to ThinCell<T>.

Safety

coerce function must ensure the returned pointer is:

• a valid unsizing of T, e.g., some dyn Trait with concrete type U
• with same address (bare data pointer without metadata) as input

pub fn leak(self) -> *mut ()

Leaks the ThinCell, returning a raw pointer to the inner allocation.

The returned pointer points to the inner allocation. To restore the ThinCell, use ThinCell::from_raw.

pub unsafe fn from_raw(ptr: *mut ()) -> Self

Reconstructs a ThinCell<T> from a raw pointer.

Safety

The pointer must have been obtained from a previous call to ThinCell::leak, and the ThinCell must not have been dropped in the meantime.

pub fn count(&self) -> usize

Returns the number of owners.

pub fn borrow(&self) -> Ref<'_, T>

Borrows the value mutably.

Returns a Ref guard that provides mutable access to the inner value. The borrow lasts until the guard is dropped.

Panics

Panics if the value is already borrowed. For a non-panicking variant, use try_borrow.

Examples

let cell = ThinCell::new(5);

{
    let mut borrowed = cell.borrow();
    *borrowed = 10;
} // borrow is released here

assert_eq!(*cell.borrow(), 10);

pub fn try_borrow(&self) -> Option<Ref<'_, T>>

Attempts to borrow the value mutably.

Returns Some(Ref) if the value is not currently borrowed, or None if it is already borrowed.

This is the non-panicking variant of borrow.

Examples

let cell = ThinCell::new(5);

let borrow1 = cell.borrow();
assert!(cell.try_borrow().is_none()); // Already borrowed
drop(borrow1);
assert!(cell.try_borrow().is_some()); // Now available

pub unsafe fn unsize_unchecked<U: ?Sized>( self, coerce: impl Fn(*const Inner<T>) -> *const Inner<U>, ) -> ThinCell<U>

Manually coerce to unsize without checks

The returned U must be a valid unsizing of T, i.e., some dyn Trait with concrete type T. &U must be a fat pointer. If not, this will fail to compile.

Safety

The ThinCell must:

• have unique ownership (count == 1)
• not be borrowed

In particular, this is the exact state after ThinCell::new.

coerce function must ensure the returned pointer:

• is a valid unsizing of T, e.g., some dyn Trait with concrete type U
• consists the same address (bare data pointer without metadata) as the input

pub unsafe fn unsize<U: ?Sized>( self, coerce: impl Fn(*const Inner<T>) -> *const Inner<U>, ) -> ThinCell<U>

Manually coerce to unsize with some checks.

Safety

coerce function must ensure the returned pointer is:

• a valid unsizing of T, e.g., some dyn Trait with concrete type U
• with same address (bare data pointer without metadata) as input

See ThinCell::unsize_unchecked for details.

Trait Implementations

impl<T: ?Sized> Clone for ThinCell<T>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: ?Sized> Drop for ThinCell<T>

fn drop(&mut self)

Executes the destructor for this type.