Is `null != variable` or `variable != null` Better in C#?

In C#, why is null != variable preferred instead of variable != null?

In C# code, the habit of using null != variable instead of variable != null stems from the historical convention of the C language.

The impact of C language on C#

In C language, the = operator represents both assignment and equality checking, which can lead to errors in which programmers accidentally use the assignment operator instead of equality checking, for example:

if (x = 5)  // 将 5 赋值给 x，而不是检查相等性

To avoid such errors, C programmers often use 5 == x to ensure that an equality check is intended.

Advantages of C#

In C#, comparison operators are strictly defined as equality checks, eliminating ambiguities in the C language. Therefore, there is no technical advantage to putting null in front of variables in equality checks.

Benefits ofvariable != null

However, the variable != null form is generally considered more readable and concise. Since null indicates the absence of a value, it makes more sense to test for its absence by declaring "if the variable is not null":

if (variable != null) ...

Conclusion

While the historical reasons for placing null before variables in C# no longer apply, the practice is still carried over from the C language. However, there are no performance or functional differences between the two forms, and the variable != null form is generally preferred for its clarity and simplicity.

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