为什么不将null评估为false？ [英] Why doesn't null evaluate to false?

问题描述

原因是 null 在条件条件下不评估为 false 是什么原因？

What is the reason null doesn't evaluate to false in conditionals?

我首先想到了赋值，以避免使用 = 而不是 == 的错误

I first thought about assignments to avoid the bug of using = instead of ==, but this could easily be disallowed by the compiler.

if (someClass = someValue) // cannot convert someClass to bool. Ok, nice

if (someClass) // Cannot convert someClass to bool. Why?

if (someClass != null) // More readable?

我认为假设 null 表示 false 。还有其他语言也使用此语言，因此我没有bug。

I think it's fairly reasonable to assume that null means false. There are other languages that use this too, and I've not had a bug because of it.

编辑：当然是指引用类型。

Daniel Earwicker对赋值错误的一个很好的评论...编译时没有警告，因为它的评估结果是 bool ：

A good comment by Daniel Earwicker on the assignment bug... This compiles without a warning because it evaluates to bool:

bool bool1 = false, bool2 = true;
if (bool1 = bool2)
{
    // oops... false == true, and bool1 became true...
}

推荐答案

这是C＃语言的特定设计功能： if 语句仅接受 bool 。

It's a specific design feature in the C# language: if statements accept only a bool.

IIRC是出于安全考虑：具体来说，这样您的第一个 if（someClass = someValue）无法编译。

IIRC this is for safety: specifically, so that your first if (someClass = someValue) fails to compile.

编辑：一个好处是，它使 if（42 = = i）约定（ yoda比较）。

One benefit is that it makes the if (42 == i) convention ("yoda comparisons") unnecessary.

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