C# 0 The Complete Reference

PART I

C h a p t e r   1 9 :  

L I N Q  

575

PART IPART I

key2.

 The result of the join is described by 

result.

 The type of 

key1

 is 

Func

,

and the type of 

key2

 is 

Func

. The 

result

 argument is of type 

Func

TInner, TResult>

. Here, 

TOuter

 is the element type of the invoking sequence; 

TInner

 is the 

element type of the passed sequence; and 

TResult

 is the type of the resulting elements. An 

enumerable object is returned that contains the result of the join.

Although an argument to a query method such as 

Where( )

 is a method compatible with 

the specified form of the 

Func

delegate, it does not need to be an explicitly declared method. 

In fact, most often it won’t be. Instead, you will usually use a lambda expression. As explained 

in Chapter 15, a lambda expression is a new syntactic feature provided by C# 3.0. It offers a 

streamlined, yet powerful way to define what is, essentially, an anonymous method. The C# 

compiler automatically converts a lambda expression into a form that can be passed to a 

Func

 parameter. Because of the streamlined convenience offered by lambda expressions, 

they are used by all of the examples in this section.