Does Using 'var' in C# Impact Performance at the IL Level?

Impact of using 'var' keyword in C# on IL level performance

In the previous question about the frequency of use of the 'var' keyword, it has been clarified that although it is only explicitly required for anonymous types, its widespread use is to improve coding speed and convenience.

Therefore, it's worth delving into the potential performance implications of using 'var' in general. Does it incur any significant overhead in intermediate language (IL) code generation?

Contrary to previous assumptions, the answer is reassuring: 'var' does not generate additional IL code. The compiler will seamlessly compile it to the appropriate type, producing the same IL result as if the type had been specified explicitly. This is because the compiler's type inference capabilities determine the correct type. Any deviation from this expected behavior will result in a compiler error.

However, it is worth noting that 'var' may cause a potential performance impact in one specific situation. When you use 'var' for a variable, the compiler will infer its exact type. However, if you manually set the type to an interface or parent type, the performance of your code may vary slightly.

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