主页 / coding / 问题 / 76919763
Accepted
Anton Tropashko
Asked: 2023-08-17 16:33:15 +0800 CST

有没有办法将assertionFailure嵌入到'??'中 表达

  • 772
TimeZone(abbreviation: "GMT+1") ?? TimeZone.current

如果我试图避免可选，如果由于某种原因产生 nil，我该如何在这里断言（内联）TimeZone(abbreviation: "GMT+1")？

像这样的东西

TimeZone(abbreviation: "GMT+1") ?? (assertionFailure("what weird runtime have you've got????"), TimeZone.current)

（这显然不能编译）

swift

2 个回答

  1. Best Answer

    尝试写下您可以处理您的情况extension的Optional地方，例如：

    extension Optional {
    func rescue(
        _ assertion: String, 
        _ fallback: Wrapped
    ) -> Wrapped {
        guard case let .some(value) = self else {
            assertionFailure(assertion)
            return fallback
        }
        
        return value
    }
}

    TimeZone(abbreviation: "GMT+1").rescue("what weird runtime have you've got????", .current) // GMT+0100
TimeZone(abbreviation: "GMT+1lalala").rescue("what weird runtime have you've got????", .current) // what weird runtime have you've got????
    • 2

  2. 我有一个使用通用函数的稍微不同的解决方案。

    import Foundation

func fail<T>(_ message: @autoclosure () -> String, fallback: T) -> T
{
    assertionFailure(message())
    return fallback
}

let x = TimeZone(abbreviation: "GMT+1") ?? fail("x is not a valid time zone", fallback: TimeZone.current)

let y = TimeZone(abbreviation: "GMT+1fdsgfds") ?? fail("y is not a valid time zone", fallback: TimeZone.current)
// On evaluating the last statement, aborts with Fatal error: y is not a valid time zone
// in a debug or playground context
    • 2

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