why does this code give EXC_BAD_ACCESS (using IMP)

Question

This code gives me EXC_BAD_ACCESS, why?

NSMutableDictionary  *d = [[NSMutableDictionary alloc] init];
IMP imp= [d methodForSelector:@selector(setObject:forKey:)          


        

Answer 1

The problem is that IMP has a return type of "id" which ARC will attempt to manage. You need to cast your function pointer to have a return type of void (consistent with the method you are calling):

    NSMutableDictionary  *d = [[NSMutableDictionary alloc] init];
    IMP imp= [d methodForSelector: @selector(setObject:forKey:)];
    void (*func)(__strong id,SEL,...) = (void (*)(__strong id, SEL, ...))imp;
    func( d,  @selector(setObject:forKey:), @"obj", @"key" );