Swift可选项-从'x'到'x'的条件强制转换警告始终会成功 [英] Swift optionals - warning on conditional cast from 'x' to 'x' always succeeds

问题描述

我想知道是否有一种方法可以关闭/避免键值为已知值的if let...NSUserDefaults结构上的xcode中的黄色"警告.

I was wondering if there is a way to turn off/avoid 'yellow' warnings in xcode on if let...NSUserDefaults constructs where the key is of a known value.

例如:

if let x = NSUserDefaults.standardUserDefaults().integerForKey("myKey") as? Int {...}

由于if let，我必须使用as?.但是，由于我使用的是已知的值类型(在这种情况下为整数)，as? Int实际上是多余的-这就是为什么我收到黄色警告"的原因.

Because of the if let I have to use as?. However, as I am using a known value type (in this case integer) the as? Int is effectively redundant - which is why I am getting the 'yellow warning'.

有什么想法吗?有没有更好的方法来编码这些类型的构造?

Thoughts? Is there a better way to code these types of constructs?

推荐答案

我的建议是解决该问题，而不是静默警告. :)

My suggestion would be to address the issue instead of silencing the warnings. :)

NSUserDefaults.standardUserDefaults().integerForKey("myKey")不返回Optional，并且类型是已知的，因此您既不需要使用if let进行可选绑定，也不需要使用as?进行类型转换.

NSUserDefaults.standardUserDefaults().integerForKey("myKey") does not return an Optional, and the type is known, so you don't need neither optional binding with if let nor type casting with as?.

就这样:

let x = NSUserDefaults.standardUserDefaults().integerForKey("myKey")

就足够了，因为如果.integerForKey无法获得实际值，它只会返回0.

will suffice, since .integerForKey just returns 0 if it can't get the actual value.

如果您不喜欢这种获取默认值的行为(我不喜欢)，请不要使用.integerForKey并将objectForKey与可选绑定一起使用，并键入强制类型转换.就像您之前所做的一样，但是用.objectForKey替换了.integerForKey.这样，如果键的值不可访问，而不是默认值，您将得到实际的nil.

If you don't like this behavior of getting a default value (I don't), then don't use .integerForKey and use objectForKey with optional binding and type casting instead. Like you were doing first but with .objectForKey replacing .integerForKey. That way you'll get an actual nil if the value for the key is unreachable, not a default value.

if let x = NSUserDefaults.standardUserDefaults(). objectForKey("myKey") as? Int {...}

这篇关于Swift可选项-从'x'到'x'的条件强制转换警告始终会成功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IT屋！