为什么人们经常看到＆QUOT;！=空可变的QUOT;代替＆QUOT;！变量=空＆QUOT;在C＃中？ [英] Why does one often see "null != variable" instead of "variable != null" in C#?

问题描述

在C＃中，有没有在你状态的条件才能在excecution速度有什么区别？

In c#, is there any difference in the excecution speed for the order in which you state the condition?

if (null != variable) ...
if (variable != null) ...

最近以来，我看到的第一个经常，这引起了我的注意，因为我是用第二个。

Since recently, I saw the first one quite often, and it caught my attention since I was used to the second one.

如果没有区别，什么是第一位的优势在哪里？

If there is no difference, what is the advantage of the first one?

推荐答案

这是一个滞留在从C.在C语言中，如果你要么使用一个糟糕的编译器或没有警告调到足够高，这将编译没有任何警告（不愧是合法code）：

It's a hold-over from C. In C, if you either use a bad compiler or don't have warnings turned up high enough, this will compile with no warning whatsoever (and is indeed legal code):

// Probably wrong
if (x = 5)

当你真正大概意思

when you actually probably meant

if (x == 5)

您可以解决这在C做：

if (5 == x)

这里的一个错字会导致无效code。

A typo here will result in invalid code.

现在，在C＃中，这是所有的废话。除非你比较两个布尔值（这是罕见的，IME），您可以编写更加易读code，作为一个如果语句需要布尔前pression入手，和类型 X = 5 是的Int32 ，而不是布尔。

Now, in C# this is all piffle. Unless you're comparing two Boolean values (which is rare, IME) you can write the more readable code, as an "if" statement requires a Boolean expression to start with, and the type of "x=5" is Int32, not Boolean.

我建议，如果你看到你的同事的code，你教育他们在现代语言的方式，并建议他们写在未来的更自然的方式。

I suggest that if you see this in your colleagues' code, you educate them in the ways of modern languages, and suggest they write the more natural form in future.

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