Question

I’m learning delegates in VB.NET and am confused about delegate types. In reading about delegates, I learned that delegates are a data type that can refer to a method with a particular kind of signature. So in the same way that a String can refer to characters, a delegate can refer to a method (for instance) that takes an integer as input and returns an integer as output. But in playing around with delegates, I found that this was not the case. The code below compiles and runs–even though I don’t obey the ‘typing’ in my delegate signature. I’m confused. Am I missing something?

Public Delegate Function myDelegate(ByVal i As Integer) As Integer' int in, rtrn int

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim md As myDelegate  'should be of type int in, rtrn int
    md = New myDelegate(AddressOf squared) 'allows assign to string in, string out
    MsgBox(md("3")) 
End Sub

Private Function squared(ByVal i As String) As String
    Return i * i
End Function

Answer 1

Yes, VB.NET is a strongly typed language, and so are delegates. But VB.NET inherits a lot of baggage from older versions of VB, such as implicit value conversion. The VB.NET compiler is emitting a call to Microsoft.VisualBasic.Conversions.ToDouble to "fix" the conflicting types.

If you put Option Strict On at the top of your .vb file, then you will see the errors that you expect.

Option Strict restricts implicit data type conversions to only widening conversions. Widening conversions explicitly do not permit any data type conversions in which data loss may occur and any conversion between numeric types and strings. For more information about widening conversions, see the Widening Conversions section.

Reference