Static vs dynamic dispatch for protocol extensions

Protocol.swift

protocol A {
	func a()
}

extension A {
	func a() {
			print("protocol extension a")
	}

	func b() {
		print("protocol extension b")
	}
}

class X: A {
	func a() {
		print("class a")
	}
	func b() {
		print("class b")
	}
}

class Y: X {
	override func a() {
		print("subclass a")
	}
	override func b() {
		print("subclass b")
	}
}


let x = X()
let y = Y()
let a = x as A
let b = y as A

x.a()
x.b()

y.a()
y.b()

a.a()
a.b()

b.a()
b.b()