Question

Suppose i have:

Public Class clsTest
   Public Sub New()
   End Sub

   Public Sub New(name_ As String)
      '...
   End Sub
End Class

I want to expand this class such:

<System.Runtime.CompilerServices.Extension> _
Public Sub methodA(t1 As clsTest, i As Integer)
    '...
End Sub

But i can not extend constructor as:

<System.Runtime.CompilerServices.Extension> _
Public Sub New(t1 As clsTest, name_ As String, i As Integer)
    '...
End Sub

Answer 1

You cannot extend constructors with an extension method. An extension method is nearly the same as a static (shared in VB) method that allows to write

instanceOfMyClass.SomeExtension(someParameter)

instead of

MyClass.SomeExtension(instanceOfMyClass, someParameter)

If you don’t have acces to clsTest(you should really change your namings) but you want to extend it anyway, you could also create a new class that inherits from it:

Public Class Foo ' consider this as your clsTest
    Public Sub New()
    End Sub
    Public Property Name As String
    Public Property Number As Int32
    Public Sub New(name As String)
        Me.Name = Name
    End Sub
End Class

Public Class Bar
    Inherits Foo

    Public Sub New(name As String, i As Integer)
        MyBase.Name = name
        MyBase.Number = i
    End Sub
End Class

Finally, maybe you don’t need to extend the class but you’re just looking for a convenient way to initialize it in an one-liner:

Dim foo = New Foo("test") With {.Number = 4711}