self.downloader = ImageDownloader()
downloader.didDownload = { [weak self] image in
    guard let strongSelf = self else {
        return
    }
    strongSelf.currentImage = image
}

self.downloader = ImageDownloader()
downloader.didDownload.delegate(to: self) { (self, image) in
    self.currentImage = image
}

class NumberPrinter {
    var numberToString = Delegated<Int, String>()
}

// somewhere inside init() or viewDidLoad() or similar
self.printer = NumberPrinter()
printer.numberToString.delegate(to: self) { (self, number) -> String in
    return self.convert(number: number)
}

self.printer = NumberPrinter()
printer.numberToString.stronglyDelegate(to: self) { (self, number) -> String in
    // will hold a strong reference to  `self`
    return self.convert(number: number) 
}

let printer = NumberPrinter()
printer.numberToString.manuallyDelegate(with: { number in
    return String(number)
})

class NumberPrinter {
    
    var numberToString = Delegated<Int, String>()
    
    func printNumber(_ number: Int) {
        // .call returns nil if no delegate was set
        guard let string = numberToString.call(number) else {
            return
        }
        print(string)
    }
    
}

var numberToString = Delegated<Int, String>()
// ...
numberToString.removeDelegate()

var numberToString = Delegated<Int, String>()
// ...
numberToString.isDelegateSet // Bool

dependencies: [
    .Package(url: "https://github.com/dreymonde/Delegated.git", majorVersion: 0, minor: 1),
]