Objective-C是否使用短路评估? [英] Does Objective-C use short-circuit evaluation?

问题描述

我尝试了以下方法:

if(myString != nil && myString.length) { ... }

得到了:

-[NSNull长度]:无法识别的选择器已发送到实例

-[NSNull length]: unrecognized selector sent to instance

在第一个条件失败后，Objective-C不会短路吗?

Does Objective-C not short-circuit after the first condition fails?

推荐答案

与C一样，Objective-C确实支持短路评估.

Objective-C does support short-circuit evaluation, just like C.

在您的示例中，似乎myString是NSNull而不是nil，因此myString != nil是正确的.

It seems that in your example myString is NSNull and not nil, therefore myString != nil is true.

NSNull 是单例，用于表示仅允许对象(例如在NSArray中)的nil.

NSNull is a singleton and is used to represent nil where only objects are allowed, for example in an NSArray.

顺便说一句，通常人们会写if (!myString && myString.length == 0).与nil相比是非常丑陋的.另外，我将长度与0进行比较.这似乎更加清楚.

Btw, normally, people write if (!myString && myString.length == 0). Comparing to nil is quite ugly. Also, I'd compare the length to 0. That seems to be more clear.

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