ProtocolExtension.swift

import Foundation

protocol MyProtocol {
    func foo()
}

class Parent {
    func foo() {
        print("parent")
    }
}

extension MyProtocol {
    func foo() {
        print("extension")
    }
}

class Child: Parent, MyProtocol {
    
}

let child = Child()
child.foo() // prints "parent" not "extension"