revised-method-chaining.swift

import UIKit

// MARK: Method chaining

class MethodChaining {
    func fetchImage() -> Fetch<UIImage> {
        let fetch = Fetch<UIImage>()
        if let image = UIImage(named: "cat.jpg") {
            if let succeed = fetch.succeed {
                // never called because its nil
                succeed(image)
            }
        }
        return fetch
    }
    
}

class Fetch<T> {
    var succeed: (T -> ())?
    func onSuccess(succeed : T -> ()) -> Self {
        self.succeed = succeed
        return self
    }
    
    func onFailure(fail : NSError? -> ()) -> Self {
        return self
    }
}

let example4 = MethodChaining()

example4.fetchImage().onSuccess { image in
    print("do something with image")
}