泛型定义

Public Class Person
   Public FirstName As String
   Public LastName As String

   Public Sub New(ByVal firstName As String, ByVal lastName As String)
      Me.FirstName = firstName
      Me.LastName = lastName
   End Sub
End Class

Public Class Company
   Public Name As String

   Public Sub New(ByVal name As String)
      Me.Name = name
   End Sub
End Class

Public Class Relation(Of T1, T2)
   Public ReadOnly Object1 As T1
   Public ReadOnly Object2 As T2

   Public Sub New(ByVal obj1 As T1, ByVal obj2 As T2)
      Me.Object1 = obj1
      Me.Object2 = obj2
   End Sub
End Class

' a new version that uses the As Class constraint

Public Class Relation2(Of T1 As Class, T2 As Class)
   Public ReadOnly Object1 As T1
   Public ReadOnly Object2 As T2

   Public Sub New(ByVal obj1 As T1, ByVal obj2 As T2)
      Me.Object1 = obj1
      Me.Object2 = obj2
   End Sub

   Public Function Contains(ByVal obj As Object) As Boolean
      Return Me.Object1 Is obj OrElse Me.Object2 Is obj

   End Function

End Class

' A new version that shows a minor issue with the VB compiler

Public Class Relation3(Of T1 As Class, T2 As Class)
   Public ReadOnly Object1 As T1
   Public ReadOnly Object2 As T2

   Public Sub New(ByVal obj1 As T1, ByVal obj2 As T2)
      Me.Object1 = obj1
      Me.Object2 = obj2
   End Sub

   Public Function Contains(ByVal obj As T1) As Boolean
      Return Me.Object1 Is obj
   End Function
   Public Function Contains(ByVal obj As T2) As Boolean
      Return Me.Object1 Is obj
   End Function

End Class


Public Class PersonCompanyRelation
   Inherits Relation(Of Person, Company)

   Public Sub New(ByVal person As Person, ByVal company As Company)
      MyBase.New(person, company)
   End Sub
End Class

Public Class PersonCompanyRelationList
   Inherits List(Of PersonCompanyRelation)
End Class