Service5.swift

/// 5. All-in-one service solution, supporting: inheritance, functional programming, delegate, default implementation.
open class Service5 {
    public init() { }
    public var inputFunction: InputFunction?
    public var outputFunction: OutputFunction?
    public weak var delegate: Service5Delegate?
    open func input() -> Bool {
        return inputFunction?() ?? delegate?.input() ?? false
    }
    open func output(text: String) {
        if let outputFunction = outputFunction {
            outputFunction(text)
        }
        else if let delegate = delegate {
            delegate.output(text: text)
        } else {
            print(type(of: self), text)
        }
    }
    public func doSomething() {
        if input() {
            output(text: "done")
        }
    }
}
public typealias InputFunction = () -> Bool
public typealias OutputFunction = (String) -> Void
public protocol Service5Delegate: class {
    func input() -> Bool
    func output(text: String)
}
public extension Service5Delegate {
    func output(text: String) -> Void {
        print(type(of: self), text)
    }
}

// Inheritance
class Client5a: Service5 {
    override func input() -> Bool {
        return true
    }
}
Client5a().doSomething() // prints "Client5a done"

// Functional programming
class Client5b {
    var input = true
    var service5 = Service5()
    init() {
        service5.inputFunction = { [unowned self] in
            return self.input
        }
    }
    func doSomething() {
        service5.doSomething()
    }
}
Client5b().doSomething() // prints "Service5 done"

// Delegate
class Client5c: Service5Delegate {
    var service5 = Service5()
    init() {
        service5.delegate = self
    }
    func input() -> Bool {
        return true
    }
    func doSomething() {
        service5.doSomething()
    }
}
Client5c().doSomething() // prints "Client5c done"