C# 5.0 Programmer's Reference

136 ❘ CHAPTER 6 Methods
TIP If you name static extension classes as in StringExtensions, it’s easy to
tell which class you are extending and that this is an extension class.
The static RemoveNonLetters method’s first parameter uses the this keyword, so you know this
is an extension method. The parameter following this has type string so this extension method
extends the string class.
The method’s code loops through a string’s characters and replaces any that are not letters with
question marks. It then returns the result.
The following code shows how a program might use this method.
string text = "When in worry or in doubt, run in circles scream and shout";
Console.WriteLine(text.RemoveNonLetters());
This code creates a string variable. It then invokes the RemoveNonLetters method just as if that
were a normal method defined by the string class.
Lambda Expressions
Lambda expressions are methods defined within the flow of the program’s code instead of as
separate methods. Often they are defined, used, and forgotten in a single statement without ever
being given a name.
You can use normal methods instead of lambda expressions, but sometimes lambda expressions
make the code simpler and easier to read. Many LINQ queries (described in Chapter 8, “LINQ”)
use functions to select values that meet certain criteria. You can write those functions as separate
methods but they may only be used once inside the LINQ query so making them separate methods
clutters the code unnecessarily.
The following sections group lambda expressions into three categories: expression lambdas, statement
lambdas, and async lambdas.
Expression Lambdas
An expression lambda consists of a list of zero or more parameters, the => operator, and a single
expression that evaluates to some result. The lambda expression returns the result of the expression.
The following code uses a simple expression lambda (in bold).
Action note = () => MessageBox.Show("Hi");
note();
Recall from the section “Delegates” in Chapter 4 that Action is a type that represents a method that
takes no parameters and returns void. The code creates a variable note with that type. It sets that
variable equal to the expression lambda defined by () => MessageBox.Show("Hi"). This lambda
www.it-ebooks.info