Module Module1

    Public Enum comparison

        theFirstComesFirst = 1
        theSecondComesFirst = 2

    End Enum

    'A simple class to hold two items
    Public Class Pair
        'Private array to hold the two objects
        Private thePair(2) As Object

        'The delegate declaration
        Public Delegate Function WhichIsFirst(ByVal obj1 As Object, ByVal obj2 As Object) As comparison

        'Passed in constructor takes two objects,
        'added in order received
        Public Sub New(ByVal firstObject As Object, ByVal secondObject As Object)
            thePair(0) = firstObject
            thePair(1) = secondObject
        End Sub

        'Public method that orders the
        'two objects by whatever criteria the objects like!
        Public Sub Sort(ByVal theDelegatedFunc As WhichIsFirst)
            If (theDelegatedFunc(thePair(0), thePair(1)) = comparison.theSecondComesFirst) Then
                Dim temp As Object = thePair(0)
                thePair(0) = thePair(1)
                thePair(1) = temp
            End If
        End Sub

        'Public method that orders the
        'two objects by the reverse of whatever criteria the
        'objects likes!
        Public Sub ReverseSort(ByVal theDelegatedFunc As WhichIsFirst)
            If (theDelegatedFunc(thePair(0), thePair(1)) = comparison.theFirstComesFirst) Then
                Dim temp As Object = thePair(0)
                thePair(0) = thePair(1)
                thePair(1) = temp
            End If
        End Sub

        'Ask the two objects to give their string values
        Public Overrides Function ToString() As String
            Return thePair(0).ToString() + ", " + thePair(1).ToString()
        End Function
    End Class


    Public Class Dog
        Private weight As Integer
        Public Sub New(ByVal weight As Integer)
            Me.weight = weight
        End Sub

        'Dogs are sorted by weight
        Public Shared Function WhichDogComesFirst(ByVal o1 As Object, ByVal o2 As Object) As comparison
            Dim d1 As Dog = DirectCast(o1, Dog)
            Dim d2 As Dog = DirectCast(o2, Dog)
            If (d1.weight > d2.weight) Then
                Return comparison.theSecondComesFirst
            Else
                Return comparison.theFirstComesFirst
            End If
        End Function

        Public Overrides Function ToString() As String
            Return weight.ToString()
        End Function
    End Class

    Class Tester
        Public Sub Run()
            'Create two students and two dogs
            'and add them to a Pair object
            Dim Milo As Dog = New Dog(65)
            Dim Fred As Dog = New Dog(12)

            Dim dogPair As Pair = New Pair(Milo, Fred)
            Console.WriteLine("dogPair" + vbTab + vbTab + vbTab + vbTab + ": {0}", dogPair.ToString())

            'Instantiate the delega
            Dim theDogDelegate As Pair.WhichIsFirst = New Pair.WhichIsFirst(AddressOf Dog.WhichDogComesFirst)

            'Sort using the delegate
            dogPair.Sort(theDogDelegate)
            Console.WriteLine("After Sort dogPair" + vbTab + vbTab + ": {0}", dogPair.ToString())
            dogPair.ReverseSort(theDogDelegate)
            Console.WriteLine("After ReverseSort dogPair" + vbTab + ": {0}", dogPair.ToString())
        End Sub
    End Class

    Sub Main()
        Dim t As Tester = New Tester()
        t.Run()
        Console.ReadLine()
    End Sub

End Module