Objective-C dynamic_cast?

Question

Is there an Objective-C equivalent of C++\'s dynamic_cast?

It can be faked using this:

MyClass *safeObject = [object isKindOfClass: [MyClass class]]
         


        

Answer 1

If you're willing to use Objective-C++, you can write this pretty easily:

template<typename T> inline T* objc_cast(id from) {
    if ([from isKindOfClass:[T class]]) {
        return static_cast<T*>(from);
    }
    return nil;
}

This should behave exactly as dynamic_cast<> except for obj-c objects.

---

If you want to stick with vanilla Obj-C you can get similar behavior with a class method on NSObject:

@interface NSObject (Cast)
+ (instancetype)cast:(id)from;
@end

@implementation NSObject (Cast)
+ (instancetype)cast:(id)from {
    if ([from isKindOfClass:self]) {
        return from;
    }
    return nil;
}
@end

This version just isn't as nice to use since you have to say something like

UIButton *button = [UIButton cast:someView];

In both versions the resulting value is nil if the cast fails.

Answer 2

Try this macro:

#define objc_dynamic_cast(obj, cls) \
    ([obj isKindOfClass:(Class)objc_getClass(#cls)] ? (cls *)obj : NULL)

And also don't forget to

#include <objc/runtime.h>

Use it like:

MyClass *safeObject = objc_dynamic_cast(originalObject, MyClass);

Answer 3

1. I don't think there is.
2. I think the space for a bug is quite small here.
3. But if you insist, a macro will do fine?