解决打字稿中的类型问题的正确方法是什么

Question

示例：

DispatchQueue.main.async()

但是Typescript编译器说，我不能将“ string”而不是“ TCountryCode”类型传递给该函数。

我的解决方法是：

func testReferences() throws {
    //Define the vars we want to test outside of the auto-release pool statement.
    weak var weakVC: UIViewController
    weak var weakNC: UINavigationController
    autoreleasepool {
        var strongVC: UIViewController? = UIViewController()
        var strongNC: UINavigationController? = UINavigationController(rootViewController: strongVC!)
        weakVC = strongVC
        weakNC = strongNC
        strongVC = nil
        
        XCTAssertNotNil(weakVC)
        XCTAssertNotNil(weakNC)
        
        strongNC = nil
    }
    //Test for nil outside of the autorelasepool statement, 
    //after the auto-release pool is drained.
    XCTAssertNil(weakVC) // fails
    XCTAssertNil(weakNC) // fails
}

或者：

// Types:
type TCountryCode = 'US' | 'RU' | 'KZ' | 'UA'
function doSomethingWithCountryCode(countryCode: TCountryCode): void => { ... }

// Code:
let countyCodes = ['US', 'RU', 'KZ', 'UA']
for (let countryCode of countryCodes) {
    doSomethingWithCountryCode(countryCode)
}

但是它似乎不正确，因为它看起来太糟而且太长了

解决此问题的正确方法是什么？

Answer 1

将countyCodes定义为const，这样它就不会自动类型扩展：

const countyCodes = ['US', 'RU', 'KZ', 'UA'] as const;

如果需要，还可以使用上面的表达式来定义类型，以减少重复：

type TCountryCode = typeof countyCodes[number];