Question

I got an object(myObject) type Object. myObject inherits of another class that contain a fonction (ImyFunction). I want to call the function, but my project need to be in “Option Strict On”. So it ask for declaration of the object.

Public MustInherit Class IClass(Of T1)
...
    Public Sub IMyFunction()
    ...


Public Class myClass1 : Inherits IClass(Of Item1)
...
Public Class myClass2 : Inherits IClass(Of Item2)




dim obj as object = new myClass1
...
obj.IMyFunction 'at this moment, I dont know whish class base of IClass I have

(its just a sample)

I cant do obj.IMyFunction because of the strict option.
Maybe there’s a cast way?

Answer 1

The MustInherit keyword does not mean that you cannot use it as a variable type, it just means that you cannot instantiate it. For instance:

Dim obj As IClass(Of Item1) = New myClass1()  ' This works
Dim obj2 As IClass(Of Item1) = New IClass(Of Item1)()  ' This will not compile 

However since, it’s generic, you have to specify the type of T1, so there’s no way to do what I think it is that you really want to do:

Dim obj As IClass = New myClass1()  ' Can't do this
obj.iMyFunction()

What I would recommend, in this case, would be to make either a non-generic base class or interface, like this:

Public Interface IInterface
    Sub IMyFunction()
End Interface

Public MustInherit Class IClass(Of T1)
    Implements IInterface
End Class

Then, you could do something like this:

Dim obj As IInterface = New myClass1()
obj.IMyFunction()