cancellable_decorator_with_curry.swift

import Foundation

class CancellableDecorator {
    
    private class Token {
        var isValid = true
    }
    
    private var token: Token?
    var delay = 0.75
    
    func scheduleCurried<Result>(_ executable: @escaping Completion<Result>) -> Completion<Result> {
        return { completion in
            self.cancel()
            let operationToken = Token()
            self.token = operationToken
            DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + self.delay) {
                if operationToken.isValid {
                    executable {
                        result in
                        if operationToken.isValid {
                            completion(result)
                        }
                    }
                }
            }
        }
    }
    
    func cancel() {
        self.token?.isValid = false
    }
    
    deinit {
        self.cancel()
    }
    
}

typealias Completion<T> = (@escaping (T) -> Void) -> Void

class Executor {
    
    func runTwoCurry(in1: String, in2: Int) -> Completion<Double> {
        return { completion in
            completion(Double(in1)! + Double(in2))
        }
    }
    
}

let decorator = CancellableDecorator()
let executor = Executor()

executor.runTwoCurry(in1: "2", in2: 1)({ result in
    String(result)
    print("\(result)")
})

executor.runTwoCurry(in1: "2", in2: 1)() { result in
    String(result)
    print("\(result)")
}

let curried = executor.runTwoCurry(in1: "2", in2: 1)
curried { result in
    String(result)
    print("\(result)")
}

decorator.scheduleCurried(curried)({ result in
    String(result)
    print("\(result)")
})