Question

I knew VB.net is very weird when talking about shadows and overloads, but this this I’m completely baffled.

I’m working with a model similar to the following one. Parent class:

Public Class Base
    Function F() As String
        Return "F() in Base Class"
    End Function

    Function F(ByVal n As Integer) As String
        Return "F(" + n.ToString() + ") in Base Class"
    End Function
End Class

and this:

Class Derived
    Inherits Base
    Shadows Function F() As String
        Return "-"
    End Function
End Class

when running the following:

Sub Main()
    Dim parent As Base = New Base()
    Dim child As Derived = New Derived()

    Console.WriteLine(parent.F())
    Console.WriteLine(parent.F(1))
    Console.WriteLine("------------")

    Console.WriteLine(child.F())
    Console.WriteLine(child.F(1)) 'this should not compile, due to the shadow keyword.

    Console.Read()
End Sub

an IndexOutOfRangeException is thrown. Moreover, when changing (in derived Class):
Return “-”
for
Return “Func in derived class”
console prints character ‘u’.
Does somebody knows the reason for this?

Answer 1

Your code is indexing a String rather than calling a function with a parameter.

Console.WriteLine(child.F(1))

This line is expanded to:

Dim childFResult As String = child.F()
Dim character As Char = F.Chars(1) ' Failure here.
Console.WriteLine(character)

Because String.Chars is the default property, you can reference it by index alone. Your string only contains one character, so there is no character at index 1.