Protocols-vs-Subclasses.swift

protocol MyProtocol {
    func methodA()
    func methodB()
}

extension MyProtocol {
    func methodA() {
        print("Default methodA")
    }
    
    func methodB() {
        methodA()
    }
}

// Test 1
protocol BaseProtocol: MyProtocol {
}

protocol SubProtocol: BaseProtocol {
}

extension SubProtocol {
    func methodA() {
        print("SubProtocol methodA")
    }
}

class SubClass: SubProtocol {}

let object1 = SubClass()
object1.methodB()
//

// Test 2
class JustClass: MyProtocol {
    func methodA() {
        print("JustClass methodA")
    }
}

let object2 = JustClass()
object2.methodB()
//
// Output
// SubProtocol methodA
// JustClass methodA