C# Null Comparisons: Should You Use 'null != variable' or 'variable != null'?

Placement of null value comparison in C#: “null != variable” and “variable != null”

In C#, when comparing variables to null, some developers prefer to use the "null != variable" format, while others choose "variable != null". Although the logical results of these expressions are the same, certain historical reasons and advantages favor the "null != variable" syntax.

Historical influence from the C language

In C, there is a potential pitfall when assigning a value to a variable in an if statement. The following C code may cause unexpected results:

<code class="language-c">if (x = 5) { ... }</code>

In this case, the "if" statement interprets the assignment as a Boolean expression, which is not expected. To avoid this problem, C programmers have adopted the practice of putting null checking first:

<code class="language-c">if (5 == x) { ... }</code>

Advantages of “null != variable”

While C#'s powerful type system eliminates the possibility of misinterpreting assignments in if statements, the "null != variable" syntax offers some advantages:

• Explicit null handling: By putting null first, it immediately indicates that you are checking for null values. This makes the code clearer and easier to understand.
• Prevent typing errors: Using "if (null != ...)" when comparing null values ​​makes it more difficult to accidentally write "null" as an unknown variable name.
• Readability: Some people find it more intuitive to read "null != variable" because it follows the natural order of evaluating whether a variable is non-null.

Conclusion

While there is no performance difference between the two syntaxes, the "null != variable" format derives from historical conventions and offers advantages in explicit null handling, protection against typing errors, and readability. Although the "variable != null" form is syntactically correct, the "null != variable" syntax is widely adopted as a best practice in C#.

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