Programming C# 3.0, 5th Edition

Implicitly Typed Local Variables

Now, let's go back to the declaration of query results where you declare the result as type var:

var result = ...

Because the select clause returns an instance of an anonymous type, you cannot define an explicit type IEnumerable<T>. Fortunately, C# 3.0 provides another feature—implicitly typed local variables—that solves this problem.

You can declare an implicitly typed local variable by specifying its type as var:

var id = 1;
var name = "Keith";
var customers = new List<Customer>(  );
var person = new {FirstName = "Donna", LastName = "Gates", Phone="123-456-7890" };

The C# compiler infers the type of an implicitly typed local variable from its initialized value. Therefore, you must initialize such a variable when you declare it. In the preceding code snippet, the type of id will be set as an integer, the type of name as a string, and the type of customers as a strongly typed List<T> of Customer objects. The type of the last variable, person, is an anonymous type containing three properties: FirstName, LastName, and Phone. Although this type has no name in our code, the C# compiler secretly assigns it one and keeps track of its instances. In fact, the Visual Studio IDE IntelliSense is also aware of anonymous types, as shown in Figure 13-1.

Figure 13-1. Visual Studio IntelliSense recognizes anonymous types

Back in Example 13-3, result is an instance of the ...