VB.NET: impossible to use Extension method on System.Object instance

Question

Can I make an Extension method for all the subclasses of System.Object (everything)?

Example:

Public Function MyExtens         


        

Answer 1

Sure you can, though you might want to be sparing about what you do here so as not to clutter every object. An extension method I like using for Object is a method called IsIn() that functions similarly to the SQL IN() statement. It's nice to say things like:

If someString.IsIn("a", "b", "c") Then
   DoSomething()
Else If someInt.IsIn(1, 2, 3) Then
   DoSomethingElse()
Else If someObj.IsIn(1, "q", #7/1/2010#) Then
   DoSomethingTheThirdWay()
End If

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EDIT -

Added implementation of IsIn() extension method below to help commenter.

Imports System.Runtime.CompilerServices

Public Module ObjectExtensions
  
  Public Function IsIn(obj As Object, ParamArray values() As Object) As Boolean
    For Each val As Object In values
      If val.Equals(obj) Then Return True
    Next
    Return False
  End Function
End Module