Cannot convert value of type '(Any) -> ()' to expected argument type '(_) -> _'

Question

Installing PromiseKit (6.2.1). Swift4.0.

import UIKit
import PromiseKit

class ViewController: UIViewController {
    func onFulfilled() -> (String) -> Promise<String> {
        return { result in
            return Promise<String> { seal in
                print(result)
                DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(1), execute: {
                    seal.fulfill("Hello")
                })
            }
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        Promise.value("first")
            .then(onFulfilled())
            .then(onFulfilled())
            .then(onFulfilled())
            .then { result in print(result) } // Cannot convert value of type '(Any) -> ()' to expected argument type '(_) -> _'
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

Error

Cannot convert value of type '(Any) -> ()' to expected argument type '(_) -> _'

How to Fix

How to fix the .then { result in print(result) }?

score 0 · Accepted Answer · answered Sep 08 '18 at 23:56

replace then with done.

_ = Promise.value("first")
            .then(onFulfilled())
            .then(onFulfilled())
            .then(onFulfilled())
            .done { result in print(result) }

see: https://github.com/mxcl/PromiseKit/blob/master/Documentation/GettingStarted.md

done is the same as then but you cannot return a promise. It is typically the end of the “success” part of the chain.

Cannot convert value of type '(Any) -> ()' to expected argument type '(_) -> _'

Error

How to Fix

1 Answers1