What's the difference between formal and informal protocols in Objective-C?

Question

What\'s the difference between formal and informal protocols in Objective-C?

Answer 1

The Objective-C language provides a way to formally declare a list of methods (including declared properties) as a protocol. Formal protocols are supported by the language and the runtime system. For example, the compiler can check for types based on protocols, and objects can introspect at runtime to report whether or not they conform to a protocol.