Struct ContextCell 

pub struct ContextCell<T> { /* private fields */ }

A thread-local cell storing a raw pointer to the current wide event.

This type provides safe methods for setting, getting, and saving/restoring the pointer, which is used by the generated guard to manage nested scopes.

Safety Invariants

The raw pointer stored in this cell is sound because:

1. The guard owns the event. The WideEvent<K> is a field of the guard, which is on the stack (or in the scope() future’s state). The guard outlives any code that calls current() within the same scope.
2. Set on creation, cleared on drop. The guard’s new sets the pointer; its Drop restores the previous pointer (or null) before the inner ScopedGuard::Drop runs.
3. Nested scopes save/restore the previous pointer via replace and the prev_ptr field on the guard.
4. No cross-thread access. thread_local! means each thread has its own cell. For async, tokio::task_local! moves with the task across threads.

The &'static lifetime returned by accessors is a “valid for the duration of the guard” lifetime — the standard pattern used by thread_local accessors (e.g., tracing’s Span::current()).

Implementations

impl<T> ContextCell<T>

pub const fn new() -> Self

Create a new cell initialized to a null pointer.

pub fn get(&self) -> Option<*mut T>

Returns the stored pointer, or None if null.

pub fn replace(&self, ptr: *mut T) -> *mut T

Sets the stored pointer. Returns the previous pointer.

pub fn clear(&self) -> *mut T

Clears the stored pointer to null. Returns the previous pointer.

pub fn restore(&self, ptr: *mut T)

Restores a previously saved pointer (typically from replace or clear).

pub unsafe fn deref_mut(&self) -> Option<&'static mut T>

Returns a &'static mut T reference to the event if the pointer is non-null.

Safety

The caller must ensure the pointer is valid and that the referenced T will not be accessed mutably from another reference for the duration of the returned borrow. In practice, this is guaranteed by the guard’s lifetime — the guard outlives all current() calls within its scope.

Trait Implementations

impl<T> Default for ContextCell<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Send for ContextCell<T>

impl<T> Sync for ContextCell<T>