Null != Variable vs. Variable != Null in C#: Does Order Matter for Performance or Readability?

Comparison of "null != variable" and "variable != null" in C#: Does order matter?

In the world of C# programming, the choice of two expressions, "null != variable" and "variable != null", has aroused the curiosity of developers. While both ultimately compute the same results, some may question whether one order has an advantage in terms of performance or inherent benefits.

The surprising answer lies in C, the language from which C# originated. A potentially harmful coding habit in C is the inadvertent use of the assignment operator ("=") instead of an equality check ("=="). Consider the following C code:

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

This code may compile without warning, although it is most likely intended to do an equality check. To avoid such errors, C programmers have developed the habit of deliberately transposing the order of comparisons to ensure that if an assignment is attempted by mistake, a syntax error occurs:

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

In C#, however, this is not necessary. The language strictly enforces the rule that "if" statements must evaluate Boolean expressions, and the assignment operator cannot provide Boolean expressions at all. This eliminates the possibility of confusion and errors.

Despite this technical reason, some C# developers may continue to use "null != variable" as a continuation of their C programming habits. However, there are no performance advantages or inherent benefits to using this order. Instead, a more natural and readable form is recommended:

<code class="language-csharp">if (variable != null)</code>

This eliminates any potential confusion and keeps the code consistent and clear.

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