A stable pointer is a reference to a Haskell expression that is guaranteed not to be affected by garbage collection, i.e., it will neither be deallocated nor will the value of the stable pointer itself change during garbage collection (ordinary references may be relocated during garbage collection). Consequently, stable pointers can be passed to foreign code, which can treat it as an opaque reference to a Haskell value.

A value of type StablePtr a is a stable pointer to a Haskell expression of type a.

Same as newStablePtr, but generalized to MonadPrim

Same as deRefStablePtr, but generalized to MonadPrim

Same as freeStablePtr, but generalized to MonadPrim

Coerce a stable pointer to an address. No guarantees are made about the resulting value, except that the original stable pointer can be recovered by castPtrToStablePtr. In particular, the address may not refer to an accessible memory location and any attempt to pass it to the member functions of the class Storable leads to undefined behaviour.

The inverse of castStablePtrToPtr, i.e., we have the identity

sp == castPtrToStablePtr (castStablePtrToPtr sp)

for any stable pointer sp on which freeStablePtr has not been executed yet. Moreover, castPtrToStablePtr may only be applied to pointers that have been produced by castStablePtrToPtr.