Struct QCellOwner

pub struct QCellOwner { /* private fields */ }

Borrowing-owner of zero or more QCell instances.

The owner will have a temporally unique ID associated with it to detect use of the wrong owner to access a cell at runtime, which is a programming error. Temporally unique means that at any one time, only one owner will hold that ID. This type derives the owner ID from the address of an internal memory allocation which this owner holds until it is dropped, which ensures that the ID is temporally unique. The allocation is aligned to ensure that its ID cannot collide with those created using QCellOwnerSeq.

In a no_std environment this requires the alloc feature because it allocates memory. For a no_std environment without alloc, consider using QCellOwnerSeq or QCellOwnerPinned.

Safety

This should successfully defend against all malicious and unsafe use. If not, please raise an issue. The same unique ID may later be allocated to someone else once you drop the returned owner, but this cannot be abused to cause unsafe access to cells because there will still be only one owner active at any one time with that ID. Also it cannot be used maliciously to access cells which don’t belong to the new caller, because you also need a reference to the cells. So for example if you have a graph of cells that is only accessible through a private structure, then if someone else gets the same owner ID later, it makes no difference, because they have no way to get a reference to those cells. In any case, you are probably going to drop all those cells at the same time as dropping the owner, because they are no longer of any use without the owner ID.

See crate documentation.

Implementations

impl QCellOwner

pub fn new() -> Self

Available on crate feature alloc only.

Create an owner that can be used for creating many QCell instances.

pub fn id(&self) -> QCellOwnerID

Available on crate feature alloc only.

Get the internal owner ID. This may be used to create QCell instances without needing a borrow on this structure, which is useful if this structure is already borrowed.

pub fn cell<T>(&self, value: T) -> QCell<T>

Available on crate feature alloc only.

Create a new cell owned by this owner instance. See also QCell::new.

pub fn ro<'a, T: ?Sized>(&'a self, qc: &'a QCell<T>) -> &'a T

Available on crate feature alloc only.

Borrow contents of a QCell immutably (read-only). Many QCell instances can be borrowed immutably at the same time from the same owner. Panics if the QCell is not owned by this QCellOwner.

pub fn rw<'a, T: ?Sized>(&'a mut self, qc: &'a QCell<T>) -> &'a mut T

Available on crate feature alloc only.

Borrow contents of a QCell mutably (read-write). Only one QCell at a time can be borrowed from the owner using this call. The returned reference must go out of scope before another can be borrowed. Panics if the QCell is not owned by this QCellOwner.

pub fn rw2<'a, T: ?Sized, U: ?Sized>( &'a mut self, qc1: &'a QCell<T>, qc2: &'a QCell<U>, ) -> (&'a mut T, &'a mut U)

Available on crate feature alloc only.

Borrow contents of two QCell instances mutably. Panics if the two QCell instances point to the same memory. Panics if either QCell is not owned by this QCellOwner.

pub fn rw3<'a, T: ?Sized, U: ?Sized, V: ?Sized>( &'a mut self, qc1: &'a QCell<T>, qc2: &'a QCell<U>, qc3: &'a QCell<V>, ) -> (&'a mut T, &'a mut U, &'a mut V)

Available on crate feature alloc only.

Borrow contents of three QCell instances mutably. Panics if any pair of QCell instances point to the same memory. Panics if any QCell is not owned by this QCellOwner.

Trait Implementations

impl Default for QCellOwner

Available on crate feature alloc only.

fn default() -> Self

Returns the “default value” for a type.

impl From<&QCellOwner> for QCellOwnerID

fn from(owner: &QCellOwner) -> Self

Converts to this type from the input type.