How to use anonymous and Lambda expression in .net



In this post I will discuss how to use anonymous and lambda expression in .net.
Imagine we have a simple example in c# that simply add two numbers.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class Program
{
    public delegate int Fn(int a, int b);
    static void Main(string[] args)
    {
        Fn add = new Fn(Add);
        Console.WriteLine(add(1, 2));
    }
    public static int Add(int a, int b)
    {
        return (a + b);
    }
}

Let’s refactor the delegate instance version of the code to use an anonymous method.
What is anonymous method?
Anonymous methods are a new language feature in C# 2.0. Anonymous methods allow us to define a code block where a delegate object is acceptable.
Let’s convert the above code using anonymous code.
Remove the following method from the delegate instance version

        public static int Add(int a, int b)
        {
            return (a + b);
        }

And replace following code with

Fn add = new Fn(Add);

With this one.
Fn add =  delegate(int a,int b)
            {
                return (a+b);
            };

Now we can write code as shown below to use the above defined class using anonymous method as follows:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


    class Program
    {
        public delegate int Fn(int a, int b);
        static void Main(string[] args)
        {
1.    Fn add = delegate(int a, int b)
2.    {
3.    return (a + b);
4.    };

            Console.WriteLine(add(1, 2));
        }

    }

Let’s go further and refactor our code using Lambda Expression.
What is lambda expression?
 Lambda expression is inline methods that are part of the Linq technology and converted to delegates or an expression tree at compile time.  Its use =>   operator to separate method. Meaning of => operator is goes to i.e. if you have a c# statement   x=>x+y  then you read this statement as x goes to x+y.
Go to the line 1 and remove the delegate keyword.


   Fn add = (int a, int b)
            {
                return (a + b);
           };
And place lambda sign => after method signature. 
 
 
   Fn add = (int a, int b)=>
            {
                return (a + b);
         };

So this final lambda expression version code looks something like this.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


    class Program
    {
        public delegate int Fn(int a, int b);
        static void Main(string[] args)
        {
            Fn add = (int a, int b) =>
            {
                return (a + b);
            };

            Console.WriteLine(add(1, 2));
        }

    }


I have summarized the above discussion into following image.


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