Saturday, December 10, 2011

Implicitly Typed Local Variables (var keyword)

You can use implicitly typed local variables whenever you want the compiler to determine the type of a local variable.
The var keyword instructs the compiler to infer the type of the variable from the expression on the right side of the initialization statement. The inferred type may be a built-in type, an anonymous type, a user-defined type, or a type defined in the .NET Framework class library.
It is important to understand that the var keyword does not mean "variant" and does not indicate that the variable is loosely typed, or late-bound. It just means that the compiler determines and assigns the most appropriate type.

The below examples show different ways in which local variables can be declared with var:

// i is compiled as an int
var i = 5;

// s is compiled as a string
var s = "Hello";

// a is compiled as int[]
var a = new[] { 0, 1, 2 };

// expr is compiled as IEnumerable
// or perhaps IQueryable
var expr = from c in customers where c.City == "London" select c;

// anon is compiled as an anonymous type
var anon = new { Name = "Terry", Age = 34 };

// list is compiled as List
var list = new List();

The var keyword may be used in the following cases as well:

* On local variables (variables declared at method scope) as shown in the previous example.

* In a for initialization statement.

for(var x = 1; x < 10; x++)

* In a foreach initialization statement.

foreach(var item in list){...}

* In a using statement.

using (var file = new StreamReader("C:\\myfile.txt")) {...}

Enjoy the programming! :)

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