Why is it impossible to declare extension methods in a generic static class?

by

Generally speaking, since you do not specify the class when you use an extension method, the compiler would have no way to know which is the class where the extension method is defined:

static class GenStatic<T>
{
  static void ExtMeth(this Class c) {/*...*/}
}

Class c = new Class();
c.ExtMeth(); // Equivalent to GenStatic<T>.ExtMeth(c); what is T?

Since extension methods themselves can be generic, this is no real problem at all:

static class NonGenStatic
{
  static void GenExtMeth<T>(this Class c) {/*...*/}
}

Class c = newClass();
c.ExtMeth<Class2>(); // Equivalent to NonGenStatic.ExtMeth<Class2>(c); OK

You can easily rewrite your example so that the static class is not generic, but the generic methods are. In fact, this is how .NET classes such as Enumerable are written.

  public static class LinkedListExtensions
  {
    public static T[] ToArray<T>(this SimpleLinkedList<T> where T:IComparable simpleLinkedList)
    {
      // code
    }
  }

More Related Contents:

  1. Can I add extension methods to an existing static class?
  2. No type inference with generic extension method
  3. Convert string to nullable type (int, double, etc…)
  4. Anonymous Types – Are there any distingushing characteristics?
  5. C# – static types cannot be used as type arguments
  6. Ambiguous call between two C# extension generic methods one where T:class and other where T:struct
  7. How can I get an extension method to change the original object?
  8. Are static members of a generic class tied to the specific instance?
  9. Why can’t I call an extension method as a static method when using static import?
  10. Pass An Instantiated System.Type as a Type Parameter for a Generic Class
  11. List or IList [closed]
  12. Check if a class is derived from a generic class
  13. Mocking Extension Methods with Moq
  14. Detect target framework version at compile time
  15. What are generics in C#? [closed]
  16. Passing dynamic object to C# method changes return type
  17. Scope of static Variable in multi-user ASP.NET web application
  18. Is there a reasonable approach to “default” type parameters in C# Generics?
  19. Interesting “params of ref” feature, any workarounds?
  20. Inheritance on a constrained generic type parameter
  21. What does denote in C# [duplicate]
  22. FindAll vs Where extension-method
  23. How to do generic polymorphism on open types in C#?
  24. Possible pitfalls of using this (extension method based) shorthand
  25. Generics: Why can’t the compiler infer the type arguments in this case?
  26. Convert List(of object) to List(of string)
  27. Casting value to T in a generic method
  28. How to convert c# generic list to json using json.net?
  29. Build c# Generic Type definition at runtime
  30. Initializing a Generic variable from a C# Type Variable

Leave a Comment