Why woud i use var in C# ?

Question

Hello..

I've been usind C# for quite some time and i am usually defining my variables with their type.

Anyway i have recently watched some tutorials and the person, that explains them is using "var" to declare variables. Why is that? Is it good for some reason or it's just a way to define a variable that you don't know the type of, at the time of declaration? If so, does Unity re-declare it, when it knows the type? Coud that bring some errors...

For example t$$anonymous$$s piece of code:

 var vertColors = new Color[mesh.vertexCount];
 
         for (var i = 0; i < mesh.vertexCount; i++)
         {
             vertColors[i] = color;
         }
 
         mesh.colors = vertColors;
         mesh.RecalculateNormals();

Why using var for declaring "vertColors"? And why isn't Unity expecting to have "var[]" for declaring an array?

The first line can be also written like t$$anonymous$$s:

 Color[] vertColors = new Color[mesh.vertexCount];

but here Unity expects me to write [], after the type of the variable. Why it doesn't give error, on the declaration (with var) above??

The tutor is also isung it to declare the "i" for the loop.. I don't get that at all...

So it seems that i can declare every type with var, instead of the type. Is that more expensive, than declaring the exact type?

As a whole, why woud i use var...

Thanks :)

Answer 1

Best Answer

Answer by Bunny83 · Oct 24, 2015 at 12:24 PM

The var keyword still declares a typed variable and it only works when you immediately assign a value to to variable. It also only works for local variables in C#. So only inside methods and not for class variables. It has no advantanges and is just a shorter way to declare a local variable.

Since you have to assign a concrete type when the variable is created it's usually clear what type it has.

Example:

 var list = new List<GameObject>();

It's especially handy for long generic type names:

 var dict = new Dictionary<string, List<GameObject>>();
 // it's equal to:
 Dictionary<string, List<GameObject>> dict = new Dictionary<string, List<GameObject>>();

You should avoid using it where the type can't be "seen" directly. Like:

 List<MyCustomClass> SomeMethod()
 {
     // ...
 }
 
 void Start()
 {
     var list = SomeMethod(); // bad example, but also works.
 }

In a lot IDEs (like Visual Studio) you can hover over the "var" keyword and it shows a popup with the inferred type.

edit
About the Color array. Color[] is a completely different type than Color. Adding square brackets to a type defines a new type. An array type with the given element type. "var" just replaces any type, no matter w$$anonymous$$ch type. Again it's just syntactical sugar. There's absolutely no difference in the compiled code whether you use "var" or not.

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instruct9r · Oct 24, 2015 at 12:31 PM 0

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Nice.. Thanks for the explanation :)

Bunny83 · Oct 24, 2015 at 12:43 PM 2

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ps: I usually don't use or recommend to use "var" in a for loop since the actual type depends on the initial value. Also since "int" is the most common type i don't see any good reason to use var over int. It might make sense when iterating through a linkedlist node like that:

 LinkedList<SomeType> list;
 for(var n = list.first; n != null; n = n.Next)

instruct9r Bunny83 · Oct 24, 2015 at 03:25 PM 3

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Honestly i don't intend to use "var" at all, since (At least in my opinion), declaring the variable with the exact type is looking better, when reviewing / updating the code later...

Thanks again, for the nice explanation :)

cheers

Why woud i use var in C# ?

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