Function atomic_xchg 

pub const unsafe fn atomic_xchg<T: Copy, const ORD: AtomicOrdering>(
    dst: *mut T,
    src: T,
) -> T

🔬This is a nightly-only experimental API. (core_intrinsics)

Stores the value at the specified memory location, returning the old value. T must be an integer or pointer type.

Safety

• If T is an integer type, this is equivalent to Atomic<T>::from_ptr followed by Atomic<T>::swap. Refer to the documentation of Atomic<T>::from_ptr for safety requirements.

• If T is a pointer type, this is equivalent to AtomicPtr<P>::from_ptr followed by AtomicPtr<P>::swap, where P is the pointee type of the pointer. Refer to the documentation of AtomicPtr<P>::from_ptr for safety requirements.

The stabilized version of this intrinsic is available on the atomic types via the swap method. For example, AtomicBool::swap.