I got a code where the specific class is implementing the protocol, the protocol has (ex: 3 methods), but the class is implementing only one of them.

protocol MyProtocol {
 func a()
 func b()
 func c()
}

class Foo: MyProtocol {
 func a() { ... }
}

and this works, but magic is if I add a new method in the protocol eg: func d(), I got an error that class Foo doesn't implement all methods of the protocol.

What is a diff between my new method func d() and others that class Foo also doesn't implement? But on my method, I got an error, and on others no...

CodePudding user response：

This means b() and c() have default implementations. If you search for extension MyProtocol in the codebase you should be able to find their default implementations.