Extending LINQ with Extensions

In LINQ, extension methods allow us to add custom functionality to the existing LINQ operators. We can create our own custom operators using extension methods and use them in our LINQ queries. In this tutorial, we'll learn how to create custom operators in LINQ using extension methods.

Syntax

public static <returnType> CustomName<TSource>(this IEnumerable<TSource> source, <parameters>)
{
     // Operator logic here
}

In the above syntax, CustomName is the name of the custom operator, <returnType> is the return type of the operator, and <parameters> are the parameters required for the operator. The this keyword before the IEnumerable<TSource> parameter indicates that the method is an extension method for the IEnumerable type.

Example

Let's create a custom operator named WhereNot that will filter out elements that do not satisfy the given condition.

public static class MyLinqExtensions
{
    public static IEnumerable<TSource> WhereNot<TSource>(
        this IEnumerable<TSource> source, Func<TSource, bool> predicate)
    {
        foreach (TSource element in source)
        {
            if (!predicate(element))
            {
                yield return element;
            }
        }
    }
}

In the above example, we defined a new extension method called WhereNot that takes an IEnumerable<TSource> and a predicate function as arguments. The method returns an IEnumerable<TSource> that contains all the elements which do not satisfy the given predicate.

Now, let's use the WhereNot operator in a LINQ query.

string[] fruits = { "apple", "banana", "cherry", "date" };
IEnumerable<string> query = fruits.WhereNot(fruit => fruit.StartsWith("c"));

In the above example, we used the WhereNot operator to filter out all the fruits that start with the letter "c".

Output

After running the above code, the output will be,

apple
banana
date

Explanation

The WhereNot operator works by iterating over the input collection and applying the given predicate function to each element. If an element does not satisfy the predicate, it is included in the output collection.

Use

Custom operators in LINQ can be useful in scenarios where the existing operators are not enough to meet our requirements. By creating our own custom operators, we can extend the functionality of LINQ to meet our specific needs.

Important Points

• Custom operators created using extension methods should follow the syntax public static <returnType> CustomName<TSource>(this IEnumerable<TSource> source, <parameters>).
• Custom operators must be declared in a static class.
• Custom operators must return an IEnumerable<TSource>.
• Custom operators can use all the LINQ operators available in the System.Linq namespace.

Summary

In this tutorial, we learned how to create custom operators in LINQ using extension methods. We saw how to define a new operator, implement it in a static method, and use it in a LINQ query. We also saw how custom operators can extend the functionality of LINQ to meet our specific requirements.