Service1.swift

// 1. Service with hardcoded input and output. Cleanest usage, but no client side extensibility (too much encapsulation).
public class Service1 {
    public init() { }
    func input() -> Bool {
        return true
    }
    func output(text: String) {
        print(type(of: self), text)
    }
    public func doSomething() {
        if input() {
            output(text: "done")
        }
    }
}
class Client1 {
    var service1 = Service1()
    func doSomething() {
        service1.doSomething()
    }
}
Client1().doSomething() // prints "Service1 done"