Question

I have a class like this:

Public Class MyClass

Private _intList As New List(Of Integer)
Private _avg As Decimal

Public Sub Add(ByVal anInt As Integer)
    _intList.Add(anInt)
End Sub

Public Property Avg() As Decimal
    Get
        Dim _sum As Integer = 0
        For Each anInt In _intList
            _sum += anInt
        Next
        Avg = If((_intList.Count > 0), _sum / _intList.Count, _avg)
        Return _avg
    End Get
    Set(ByVal value As Decimal)
        If _avg <> value Then
            _avg = value
            Console.WriteLine("Value changed")
        End If
    End Set
End Property

End Class

The Getter is calculating average and calls Setter to save the value. For some reason I cannot understand, the average is always 0. For example:

Dim c As New Class2()
c.Add(1)
c.Add(2)
c.Add(3)
Console.WriteLine(c.Avg.ToString()) ' This will print 0

Did I do something wrong? What is the cause of this?

Answer 1

This is by design and explicitly mentioned in the Visual Basic Language Specification, chapter 9.7.1:

A special local variable, which is implicitly declared in the Get
accessor body’s declaration space with the same name as the property,
represents the return value of the property. The local variable has
special name resolution semantics when used in expressions. If the
local variable is used in a context that expects an expression that is
classified as a method group, such as an invocation expression, then
the name resolves to the function rather than to the local variable.
For example:

ReadOnly Property F(i As Integer) As Integer
    Get
        If i = 0 Then
            F = 1    ' Sets the return value.
        Else
            F = F(i - 1) ' Recursive call.
        End If
    End Get
End Property

Solve your issue by assigning the _avg field directly. Property getters with side-effects like this is best avoided.