Imports System

Public Module Module1

    private o3 as object

    Public Sub Main()

        Console.WriteLine("Hello World")

​

        Dim value As New Test(Of DateTimeOffset?)

        Console.WriteLine(value.Value is nothing)

        Dim dt1 As New DateTimeOffset(2017, 1, 1, 1, 1, 1, TimeSpan.Zero)

        Dim dt2 As New DateTimeOffset(2017, 1, 2, 1, 1, 1, TimeSpan.Zero)

​

        Console.WriteLine(value.TrySetValue(Nothing, dt1))

        Console.WriteLine(value.Value = dt1)

​

        Console.WriteLine(value.TrySetValue(Nothing, dt2))

        Console.WriteLine(value.Value = dt1)

        Console.WriteLine(value.TrySetValue(dt1, dt2))

    End Sub

End Module

​

public class Test(Of T)

​

    Public readonly Property Value As T

        Get

            Return CType(Threading.Volatile.Read(_value), T)

        End Get

    End Property

    Private _value As Object

​

    Public Function TrySetValue(oldValue As T, newValue As T) As Boolean

        Dim curValObj As Object = Threading.Volatile.Read(_value)

        If Not Object.Equals(CType(curValObj, T), oldValue) Then Return False

        Dim newValObj = CObj(newValue)

        Return Object.ReferenceEquals(Threading.Interlocked.CompareExchange(_value, newValObj, curValObj), curValObj)

    End Function

end class