' This demonstrates letting you use any type with a GetEnumerator() method

' with the link operators, even if it doesn't implement IEnumerable, by

' just calling .AsEnumerable(Of T)(). This is useful in a few sitations,

' including a number of Office Interop types or other places where 

' you have old pre-.Net collection objects.

​

' Note, uncommenting below line causes compiler error (Option Strict must be OFF) :(

' Option Strict On

​

'Therefore, I recommend isolating the Extension class to its own file

​

Imports System

Imports System.Collections.Generic

Imports System.Runtime.CompilerServices

Imports System.Linq

​

Public Module Module1

    Public Sub Main()

        ' TestObject does NOT implement IEnumerable

        Dim t As New TestObject()

        ' But it does have a GetEnumerator() method. We can still use a For Each Loop

        For Each u As Integer In t.AsEnumerable(Of Integer)()

            Console.WriteLine(u)

        Next

        ' And we can also filter out the odd digits with Where() (as well as any other linq method we wanted)  

        Console.WriteLine(t.AsEnumerable(Of Integer)().Where(Function(d) d Mod 2 = 0).Sum())

    End Sub

End Module

​

' Does NOT implement IEnumerable

Public Class TestObject

    Dim digits() As Integer = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}

    ' I could just "Return digits", but I wanted to prove we didn't need a "real" collection type

    Public Iterator Function GetEnumerator() As IEnumerable(Of Integer)

        For Each d As Integer In digits

            Yield d

        Next

    End Function

End Class

​

Public Module Extensions

    ' Requires Option Strict Off, so the compiler will make the implied GetEnumerator() call :(

    <Extension()> 

    Public Iterator Function AsEnumerable(Of T)(input As Object) As IEnumerable(Of T)        

        For Each item As T In input.GetEnumerator()

            Yield item

        Next

    End Function

​

End Module