c#
////////////////

public static class Extensions
{
    public static string GetFirstThreeCharacters(this String str)
    {
        if(str.Length < 3)
        {
            return str;
        }
        else
        {
            return str.Substring(0,3);
        }
    }
}

vb.net

<System.Runtime.CompilerServices.Extension> _
Public Function GetFirstThreeCharacters(Byval str As String) As String
If str.Length < 3 Then
	Return str
Else
	Return str.Substring(0, 3)
End If
End Function

oop features in vb6
//////////////////////
http://cs.iupui.edu/~aharris/avb/avb4/oop.html

https://books.google.co.th/books?id=kVqB5hjNsScC&pg=PA345&lpg=PA345&dq=visual+basic+6+oop&source=bl&ots=19WwyyRM-D&sig=sC5sSwF-kfDbTW5NIKu8oAd3mHI&hl=en&sa=X&ved=0ahUKEwjtqrHMp5HKAhXECo4KHbkIB4cQ6AEIVTAJ#v=onepage&q=visual%20basic%206%20oop&f=false