See how many you can get right before running it... :D

ProtocolExtensionQuiz.swift

//: Playground - noun: a place where people can play

import UIKit

// PROTOCOL

protocol Foo {
    func foo() -> String
    func baz() -> String
}

extension Foo {
    func foo() -> String {
        return "foo"
    }

    func bar() -> String {
        return "bar"
    }

    func baz() -> String {
        return "baz"
    }
}

// STRUCT

class MyFoo: Foo {
    func foo() -> String {
        return "myfoo"
    }

    func bar() -> String {
        return "mybar"
    }
}

class MySubFoo: MyFoo {
    func foo() -> String {
        return "mysubfoo"
    }
    
    func baz() -> String {
        return "mybaz"
    }
}

// CODE

// An instance of MyFoo
let superA = MyFoo()
// Same thing, but cast to Foo (the protocol)
let superB: Foo = superA

// An instance of MySubFoo
let subA: MySubFoo = MySubFoo()
// Same thing, but cast to MyFoo (the superclass)
let subB: MyFoo = subA
// Same thing, but cast to Foo (the protocol)
let subC: Foo = subA

superA.foo() // = ?
superB.foo() // = ?
subA.foo() // = ?
subB.foo() // = ?
subC.foo() // = ?

superA.bar() // = ?
superB.bar() // = ?
subA.bar() // = ?
subB.bar() // = ?
subC.bar() // = ?

superA.baz() // = ?
superB.baz() // = ?
subA.baz() // = ?
subB.baz() // = ?
subC.baz() // = ?