Question

My question may seem strange, but i wanna to get this idea around Stackers’ minds, in my work i just noticed that every protocol is conformed by a class all the time, i wondered about the possibility to make a simple object conforms to protocols too, and if not (and almost not ), why not ??

Appreciate your concern

Answer 1

There are two parts to protocol conformance:

• the object must respond to the required messages in the protocol definition
• the object must return YES when asked whether it conforms to the protocol

So, can we arrange for an instance of NSObject to satisfy those two conditions? Yes. In fact, there are at least two ways to do so. First, let’s make all instances of NSObject conform to the protocol. What we do is to define the protocol methods in a category on NSObject, which solves the first part. Then we “swizzle” (which means using the class_replaceMethod() runtime function) -[NSObject conformsToProtocol:], returning YES for our interesting protocol.

Now let’s imagine that you want to make a specific instance of NSObject conform to the protocol. This is slightly easier. First, create a subclass of NSObject that conforms to the protocol and implements the required methods; there’s no need to override -conformsToProtocol: because the runtime library can see that this class conforms. Now, at runtime, take your NSObject instance and call object_setClass() to switch its class to your conforming subclass.