Swift 优化级别中断将 NSArray 转换为 Array

本文介绍了Swift 优化级别中断将 NSArray 转换为 Array的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

当 Swift Optimization Level 设置为 None [-Onone](调试的默认值)时，以下(有些人为的)代码有效:

The following (somewhat contrived) code works when Swift Optimization Level is set to None [-Onone] (default for debug):

    let nsa = NSArray(array: ["foo", "bar"])
    let a = nsa as [String]

但应用程序在运行时崩溃(崩溃日志)设置为最快 [-O](默认发布).

But the app crashes (crash log) during run-time when set to Fastest [-O] (default for release).

我幸运地发现我可以通过这样做来解决这个问题:

I luckily discovered I can work around the issue by doing this:

    let a = nsa as [AnyObject] as [String]

我的问题有两个:

你能帮我理解为什么会这样吗?
是否有更好的方法将 NSArray 转换为数组?

更新

这似乎是一个错误.我没有向苹果报告.如果其他人愿意花时间这样做，请这样做！

UPDATE

This does seem to be a bug. I have not reported it to Apple. If someone else would like to take the time to do so, please do!

推荐答案

它似乎已在 Xcode Version 6.3.1 (6D1002) 上修复.

It seems to be fixed on Xcode Version 6.3.1 (6D1002).

而且，这不是您原来问题的答案，而是随着新 Swift 1.2 的引入，as 是强制转换，现在被更明确的 as! 取代.你应该期待 NSArray 到 Array 其中 T != AnyObject 或 NSObject 崩溃.

And, not an answer to your original problem but as the new Swift 1.2 introduced, as is a forced cast, now replaced by more explicit as!. You should expect an NSArray to Array<T> where T != AnyObject or NSObject to crash.

你最好使用条件转换 as?.尽可能避免 !.

You'd better use conditional cast as?. Avoid ! any time it's possible.

let nsa = NSArray(array: ["foo", "bar"])
if let a = nsa as? [String] {
    println("a \(a)")
}

这篇关于Swift 优化级别中断将 NSArray 转换为 Array的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！