The “var” thing

I’ve come to really enjoy using the “var” keyword in C#. Although it’s been written about many times, I want to clarify what it is.

C# is a strongly-typed language, which means that every variable you declare must have a specified type. You must say it’s an integer or a string or a Thing. “var” does not change that.

“var” looks a lot like the var in Javascript. Javascript is not strongly-typed, so you don’t have to say what “x” represents. Maybe it’s an integer at the moment and a string later. You don’t have to decide.

But let’s be clear: var in C# has nothing to do with var in Javascript. C#’s “var” is a syntactic shortcut, and nothing more. Your variable is still strongly typed.

Here is a typical piece of C# code: List<Thing> myThingList = new List<Thing>();

Notice something redundant in there? We said List<Thing> twice.

Since the right side of that assignment will always result in a List<Thing>, why do we need to say so on the left side? Thus: var myThingList = new List<Thing>();

The compiler knows that myThingList will always be a List<Thing>. So it can unambiguously (strongly) type it as such. No need for us to spell it out.

So I find that var is a nice thing for more terse code. And if I decide that myThingList should actually be an array, I just need to change it one place.