C# 0 The Complete Reference

Expression Lambdas

In an expression lambda, the expression on the right side of the 

=>

 acts on the parameter (or 

parameters) specified by the left side. The result of the expression becomes the result of the 

lambda operator and is returned.

Here is the general form of an expression lambda that takes only one parameter:

param

 => 

expr

When more than one parameter is required, then the following form is used:

(

param-list

) => 

expr

Therefore, when two or more parameters are needed, they must be enclosed by parentheses. 

If no parameters are needed, then empty parentheses must be used.

Here is a simple expression lambda:

count => count + 2

Here 

count

 is the parameter that is acted on by the expression 

count + 2

. Thus, the result is 

the value of 

count

 increased by two. Here is another example:

n => n % 2 == 0

In this case, this expression returns true if 

n

 is even and false if it is odd.

To use a lambda expression involves two steps. First, declare a delegate type that 

is compatible with the lambda expression. Second, declare an instance of the delegate, 

assigning to it the lambda expression. Once this has been done, the lambda expression can 

be executed by calling the delegate instance. The result of the lambda expression becomes 

the return value.

The following program shows how to put the two expression lambdas just shown into 

action. It declares two delegate types. The first, called