Bitwise pointer swapping. Useful for, say, a producer-consumer mutually recursive trampoline

bitwise_pointer_swapping.h

static void(^swap_pointers)(void) =
^{
    typedef typeof(unsigned long(^)(unsigned long)) predicate_function;
    typedef typeof(unsigned long(^*)(unsigned long)) predicate_function_t;

    predicate_function func_a, func_b;
    __block void * current = (predicate_function_t)&func_a;
    __block void * swap    = (predicate_function_t)&func_b;
    
    func_a = ^ unsigned long (unsigned long predicate) {
        printf(" func_a returned ");
        return predicate;
    };
    
    func_b = ^ unsigned long (unsigned long predicate) {
        printf(" func_b returned ");
        return predicate;
    };
    
    printf("Invoked current(11) and");
    printf("%lu.\n", (*((predicate_function_t)(current)))(11));
    printf("Swapped current with swap and then ");
    (predicate_function_t)({ swap = (uintptr_t)swap ^ (uintptr_t)current ^ (uintptr_t)(current = (uintptr_t)swap); swap; });
    printf("invoked current again (with a value of 24):");
    printf("%lu\n", (*((predicate_function_t)(current)))(24));
};