C# - Extension method usage

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Extension methods enable you to “add” methods to existing types without creating a new derived type, recompiling, or otherwise modifying the original type.

Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type.

The most common extension methods are in LINQ; Linq provides two classes: Enumerable and Queryable. And their extensions methods operate on IEnumerable and IQueryable.

Extension methods are static methods who reside in static utility classes.

For example:

public static bool IsNull(this object x)
    return x == null;
public static bool IsNullOrEmpty(this object text)
    return text == null || (string)text == "";
public static IEnumerable<int> GetOddMembers(this List<int> list)
    return list.Where(x => x%2 != 0);


object y = null;
Console.WriteLine(y.IsNull()); //True
y = new object();
Console.WriteLine(y.IsNull()); //False

object s = null;
Console.WriteLine(s.IsNullOrEmpty()); //True
s = string.Empty;
Console.WriteLine(s.IsNullOrEmpty()); //True
s = "hello";
Console.WriteLine(s.IsNullOrEmpty()); //False

Console.WriteLine(IsObjectNull.IsNullOrEmpty(null)); //True

List<int> list = new List<int>() {1, 2, 5, 7, 12};
var oddMembers = list.GetOddMembers();
foreach (var oddMember in oddMembers)
    Console.WriteLine(oddMember); //1 5 7

I Hope this can do help to you!

Enjoy coding!

SUN Jiangong

SUN Jiangong

A senior .NET engineer, software craftsman. Passionate about new technologies.