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When to Use and Not Use Variable Type var in C#

Settling the Debate Surrounding var and C#

Many languages, particularly scripting languages, have a loosely typed variable type named var. In these languages, var can hold any type of data. If you place a number into a var then it will be interpreted as a number whenever possible. If you enter text it will be interpreted as a string, etc. var can even hold various objects and will behave properly.

As you probably already know, C# has supported the variable type var since version 3.0. Ever since, the debate has raged on: you should always use var; you should never use var. There are arguments for both sides that sound good, as we’ll see below. What I will say is that it depends. I propose that there are places to use var and places not to use var.

One important point to remember with C#, however, is that var is strongly typed. Once a var is declared it can only be of the type with which it was initialized. And a var must be initialized in order to be declared.

Some Arguments for Variable Type var

  • var requires less typing. It also is shorter and easier to read, for instance, than Dictionary<int,IList>.
  • var requires less code changes if the return type of a method call changes. You only have to change the method declaration, not every place it’s used.
  • var encourages you to use a descriptive name for the variable. This means the instance, not the type name. For instance:
    • var customer = new Customer() rather than var c = new Customer().

Some Arguments Against Variable Type var

  • var obscures the actual variable type. If the initializer doesn’t return a clearly defined type then you may not be able to tell the variable’s type.
  • Using var is lazy. While var is certainly easier to type than Dictionary<int,IList>, if the variable isn’t named well, you’d never know what it refers to.
  • Using var makes it hard to know what type the underlying variable actually is. Again, a properly named variable speaks for itself.
  • var can’t contain nullable types such as int?. This is actually untrue as you can cast a value to a nullable type
    • var nullableInt = (int?)null;

How I Use var

Although I agree with some of the arguments above, I have fairly specific rules that I use to determine whether I will use var or specify the type literally.

I use var any time that the initialization of the variable clearly tells me what the variable will contain.

var count = 17;
var primeNumbers = new [] { 2, 3, 5, 7, 11, 13, 17 };
var customer = new Customer();
var activeOrders = GetAllOrders().Where(o => o.Active);
foreach (var activeOrder in activeOrders) { … }Code language: JavaScript (javascript)

Note that in all of these cases, the variable names are descriptive and the initializer is clear. I also pluralize enumerations and arrays.

Cases where I do not use var, even though I still name the variable descriptively, are when the initializer is not clear.

decimal customerBalance = GetCustomerBalance();
CustomerStatus customerStatus = GetCustomerStatus();

I declare customerBalance as decimal to know its type for clarity. Reasonable alternatives might include double or even int or long. The point is, I don’t know by looking at the code.

I declare customerStatus as the Enum that it is. This makes it clear there are a limited number of possible values that can be referenced or tested by name.

Michael Brennan, in his blog post Why You Should Always Use the ‘var’ Keyword in C#, makes some compelling points. I recommend it for further reading. However, I prefer the clarity of specifying otherwise obscure types just to make things as clear as possible to the reader who may have to maintain my code in the future.

Want More?

Curious about how else variables are utilized? Check out our blog Painless Bug Testing through the Isolation of Variables!

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