Function overloads based on interface inheritance

Question

Say I have a base interface, and another one inheriting from it :

Public Interface Parent
    {stuff}
End Interface

And

Public Interface Child
    Inherits Parent
    {other stuff}
End Interface

I also have a sub and its overload :

Public Sub doStuff(parameter As Parent)
     {do some stuff}
End Sub 

And

Public Sub doStuff(parameter As Child)
     {do some other stuff}
End Sub 

If I call the sub like this it calls the "child function" :

Dim myParam As Child = New SomeClassImplementingChild
doStuff(myParam)

However, is there any way to make it call the "child function" with something like this, assuming I don't know at compile time the type of the coolParameter :

Public Sub coolFunction(coolParameter As Parent)
    doStuff(coolParameter)
End Sub 

Dim myParam As Child = New SomeClassImplementingChild
coolFunction(myParam)

Answer 1

I have found a workaround which is I guess the closest I'll ever get to a solution:

doStuff(Convert.ChangeType(coolParameter, coolParameter.GetType))

That will convert to the "real" type at Runtime, effectively calling the right function. However, the functions all have to be public to be called that way