Injection

injection.swift

import Cocoa

let x = "Face"

protocol Injection<T, U> {
    func apply(T) -> U
    func invert(U) -> T?
}

class IntInjection: Injection {
    func apply(i: Int) -> String {
        String(i)
    }
    func invert(s: String) -> Int? {
        s.toInt()
    }
}