>>13635047Declares an identifier 'op' that's a pointer to a function taking a void pointer and returning a void pointer.
You could, for instance, have multiple memory allocators and set 'op' to point to the desired free() function. Or you could, for instance, have a state machine taking and returning state-specific data, with 'op' pointing to the function for the current state. Or you could, for instance, have a structure representing an entry in an interrupt vector table, with 'op' pointing to the interrupt handler for that entry.
