Question

I found that I could do such things in objc:

Protocol* aProtocol = @protocol(NSObject);

but what is this technique used for?

Answer 1

You could have, for example, a container that offers a service to check that all of its contents conform to a protocol.

Protocol *contentProtocol;

- (void)setContentProtocol:(Protocol *)proto;

Then the user of the container could call:

[container setContentProtocol:@protocol(MyProtocol)];

And somewhere in the container the check could be made:

[[item class] conformsToProtocol:contentProtocol];