无法将类型“(Any) -> ()”的值转换为预期的参数类型“(_) -> _”

Question

正在安装 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()
    }
}

错误

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

如何修复

如何修复 .then { result in print(result) }？

Answer 1

将 then 替换为 done。

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

参见：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.