Req17: Define extension methods in an "extension class" of the extended type

[This post is part of a series, "wish-list for future versions of VB"]

IDEA: Allow extension methods to be defined in their "extension class". It would look like this:

    Dim x = "hello"

    x.LogToDisk() ' extension method defined on strings

    Dim y = x.p ' extension property defined on strings

    <Runtime.CompilerServices.Extension>

    Class String

        <Runtime.CompilerServices.Extension()>

        Sub LogToDisk()

            My.Computer.FileSystem.WriteAllText("c:\log.txt", Me, True)

        End Sub

        <Runtime.CompilerServices.Extension()>

        ReadOnly Property p As Integer

            Get

                Return Me.Length + 42

            End Get

        End Property

    End Class

 This would be a useful syntax for defining extension properties. It would also allow tricks like the following: code that looks like a method, but is robust against being called on a "null reference".

Class Fred

    <Runtime.CompilerServices.Extension()>

    Function ToString2() As String

        If Me Is Nothing Then Return "_"

        Return Me.ToString()

    End Function

    Public Overrides Function ToString() As String

        Return "hello fred"

    End Function

End Class

Provisional evaluation from VB team: It's bad enough that extension methods currently work on a null "Me" pointer already. We don't think it's good language design to make such a thing even easier: it feels like it would lead to more confusion than readability.