c# - Use of "var" type in variable declaration

Question

Our internal audit suggests us to use explicit variable type declaration instead of using the keyword var. They argue that using of var "may lead to unexpected results in some cases".

I am not aware of any difference between explicit type declaration and using of var once the code is compiled to MSIL.

The auditor is a respected professional so I cannot simply refuse such a suggestion.

Answer 1

How about this...

double GetTheNumber()
{
    // get the important number from somewhere
}

And then elsewhere...

var theNumber = GetTheNumber();
DoSomethingImportant(theNumber / 5);

And then, at some point in the future, somebody notices that GetTheNumber only ever returns whole numbers so refactors it to return int rather than double.

Bang! No compiler errors and you start seeing unexpected results, because what was previously floating-point arithmetic has now become integer arithmetic without anybody noticing.

Having said that, this sort of thing should be caught by your unit tests etc, but it's still a potential gotcha.