// MARK: Minimal code from ReactiveCocoa/ReactiveSwift

public protocol SignalProtocol {
    associatedtype Value
    associatedtype Error: Swift.Error

}
extension SignalProtocol where Error == NoError {
    /// - Note: Return value is Optional + non-Void type.
    @discardableResult
    public func observe() -> Bool? {
        return true
    }
}

public enum NoError: Swift.Error { }

public final class Signal<V, E: Swift.Error>: SignalProtocol {
    public typealias Value = V
    public typealias Error = E

    public init() {}
}

// MARK: Main

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

        let signal = Signal<(), NoError>()
        signal.observe() // OK, no warning

        let optSignal: Signal<(), NoError>? = Signal<(), NoError>()
        optSignal?.observe()    // Bad, unused warning in Swift 3 (Xcode 8)

        return true
    }

}