Lambda Expression in C# 3.0

Lambda Expression is the one of the best feature of the C# 3.0. Lambda expression is same as anonymous method introduced in C# 2.0. Lambda Expression is a concise syntax to achieve the same goal as anonymous method. Now we can summarize Lambda expression in one line.

“Lambda expression is simply a Method.”

Syntax of Lambda Expression

Input Parameters => Expression/Statement Block;

Left hand side of expression contains the zero or more parameters followed by Lambda operator ‘=>’ which is read as “goes to” and right hand side contains the expression or Statement block.

A simple Lambda expression: x => x * 2

This Lambda expression is read as “x goes to x times 2”. Lambda Operator “=>” has sameprecedence as assignment “=” operator. This simple expression takes one parameter “x” and returns the value “x*2”.

Parameters Type

The parameters of the lambda expression can be explicitly or implicitly typed. For example

(int p) => p * 4; // Explicitly Typed Parameter
q => q * 4; // Implicitly Typed Parameter

Explicit typed parameter is same as parameters of method where you explicitly specified the type of parameter. In an implicit typed parameter, the type of parameter inferred from the context of lambda expression in which it occurs.

Type Inference is a new feature of c# 3.0. I will explain it in some other blog.

Use simple Lambda Expression

Here is simple example of Lambda Expression which returns a list of numbers greater than 8.

int[] numbers = {1,2,3,4,5,6,7,8,9,10 };  
var  returnedList = numbers.Where(n => (n > 8));

You can also use anonymous method for returning same list.

int[] numbers = {1,2,3,4,5,6,7,8,9,10 };
var returnedList = numbers.Where(delegate(int i) { return i > 8; });

Use Statement Block in Lambda Expression

Here is simple example to write statement block in the lambda expression. This expression returns list of numbers less than 4 and greater than 8.

int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

var returnedList = numbers.Where(n =>
                          {
                            if (n < 4)
                                  return true;
                              else if (n > 8)
                                  return true;

                              return false;
                          }
                       );

Use Lambda with More then one Parameter

You can also write lambda which takes more than one parameters. Here is an exampleof lambda which adds two integer numbers.

delegate int AddInteger(int n1, int n2);

AddInteger addInt = (x, y) => x + y;
int result = addInt(10,4); // return 14

Use Lambda with Zero parameter

Here is an example of lambda which take no parameter and returns new Guid.

delegate Guid GetNextGuid();

GetNextGuid getNewGuid = () => (Guid.NewGuid());
Guid newguid = getNewGuid();

Use Lambda that return Nothing

You can also write lambda which returns void. Here is an example that lambda is only showing message and return nothing.

delegate void ShowMessageDelegate();

ShowMessageDelegate msgdelegate = () => MessageBox.Show("It returns nothing.");
msgdelegate();

Some Build in Delegates

Dot Net Framework 3.0 provides some build in parameterized delegate types that is “Func<t>(...)” and also provides some parameterized delegates that returns void that is “Action<T>(...)”.

Extension Method

Last Few days I was thinking how Microsoft added new method in existing classes of visual studio. I was surprised because I was creating List<> and I was showing me some LINQ methods, but when I commented “Using System.Linq” line, it was showing me default list methods.

But when is removed comments “Using System.Linq”. Now Visual Studio was showing me some Linq methods in the intelligence window.

Then I started searching on the web about it. I found new exciting feature of framework 3.0, which is “Extension Methods”. You can extend existing classes without inheritance using extension methods. There are some which you should keep in mind while writing extension method.

1. You cannot override existing method by writing extension method.
   
2. If extension method has same name as instance method then it will not called, because the priority of instance method is high. At compile time extension method has low priority.
   
3. You can write extension for Properties, data Members and events.
   

It is very simple to write extension method. Create static class and write static extension method in this class. The “this” keyword in the parameters tells the compiler to add the extension method in the type after “this” keyword. In my example “this string” compiler adds extension method to the string class.

namespace ExtensionTest
{
 public static class ExtensionOfString
 {
   public static bool IsNumber(this string value)
   {
       Regex expression = 
             new Regex(@"^[0-9]([\.\,][0-9]*)?$");
       return expression.IsMatch(value);
   }
 }
}

Here is an example to use extension method. Include the namespace and call your extension method like the original method of the instance.

 using ExtensionTest;
. . . . .

string number = "4";
bool isNumber = number.IsNumber();

You can see how easy it is to write extension method in Dot net.