gistfile1.m

    NSNumber *a;
    NSNumber *b;
    
    NSArray *os = @[ [NSValue valueWithPointer:&a],
                     [NSValue valueWithPointer:&b] ];
    
    for (int i = 0; i<2; i++) {
        void *pointer = [[os objectAtIndex:i] pointerValue];
        NSNumber *a_ptr_1 = (__bridge NSNumber*)pointer;

        NSNumber **a_ptr_2; // ???
        a_ptr_2 = pointer;
        *a_ptr_2 = @2.0;