Question

In Objective-C, it is possible to pass a class as a parameter to a method:

- (void) methodThatTakesClass:(Class)theClass;

And it is possible to pass an instance that is conforming to a protocol as a parameter:

- (void) myConformInstance:(id <MyProtocol>)theObject;

Is it possible to use the combined functionality? A method which takes a class which is conforming to a certain protocol.

Answer 1

Yes. The following is a valid program which will log the NSObject class.

#import <Foundation/Foundation.h>
void f(Class <NSObject> c) {
    NSLog(@"%@",c);
}
int main() {
    f([NSObject class]);
}

This would cause a compiler error if you tried to pass a class which doesn’t conform to NSObject, such as the Object class. You can also use it for methods.

- (void)printClass:(Class <NSObject>)c;