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Secrets of Extension Methods: Part II

Posted by Sateesh Arveti Articles | Visual C# December 23, 2008
This article explains how Extension Methods are used in LINQ.
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In previous article, I had discussed about Extension methods. Now, we will look into implementation of Extension Methods in LINQ. I designed this application in Visual Studio 2008 using Console Applications.

Introduction to LINQ:


LINQ is a new technology that will allow writing Queries in C# itself. It's based on Query Expressions. Query Expressions uses declarative query syntax. It means, we will just specify what we want without bothering about specification of how to get it. By using Query Expressions, we can write queries in C#, which are type safe. LINQ makes a Query a built-in construct of C# just like a class or struct. LINQ uses Extension Methods in its internal implementation of Query Operators like GroupBy, OrderBy etc.

Steps to understand LINQ's Extension Methods:

  1. Create a new Console Application and name it as LinqExtensions.
     
  2. By default System.Linq will be imported.So,just remove that entry.
     
  3. Now, in Main method,write this lines:

    int[] marks = {10,20,30,405,50 };
     
  4. If we see the methods available on marks are very few.
     
  5. Now, include System.Linq namespace, we will see lot of methods that are new. This is possible, because of Extension methods present in that namespace.
     
  6. System.Linq namespace is having definition for the extension methods that can be called on marks object.
     
  7. LINQ uses Extension methods in this approach.

Finally, this class looks like this:



Here Max is an extension method present in System.Linq namespace.

This extension methods present in Linq can be used on any type that implements IEnumerable(T).

Some of the Extension methods in LINQ accept Lambda expressions as a parameter.

Lambda Expression is a function without a name, but having expressions and statements in it.

We will look into Lambda expressions in coming article.

           var sortedMarks = marks.OrderBy(m => m);
            foreach (var mark in sortedMarks)
            {
                Console.WriteLine(mark);
            }

Above statements, will sort the list by using Extension Method OrderBy present in System.Linq namespace and having lambda expression as a parameter.

Internal Implementation:


If we disassemble this code, we can see the call to extension method will be like this:

Call int32 [System.Core]System.Linq.Enumerable::Max(class [mscorlib]System.Collections.Generic.IEnumerable`1<int32>)

Summary:


So, LINQ uses Extension Methods in its Query operators like OrderBy, GroupBy etc.

I am attaching the code for reference. I hope this will be useful for all.

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