で、できた。。 #cswift #CodePiece

CodePiece.swift

import UIKit

protocol CustomViewControllerType {
    func hello()
}
extension CustomViewControllerType {
    func hello() {
        print("hello")
    }
}
extension ViewController : CustomViewControllerType {
    func hello() {
        (self as CustomViewControllerType).hello()
        print("yellow")
    }
}
class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        hello()
    }
}