why not inherit from type 'b(Of a)'

14 May 2009 9:53 PM

×“× ×™

Public Class Form1
        Public Class a

        End Class
        Public Class a1
            Inherits a
        End Class
        Public Class a2
            Inherits a
            Private dsfs As d(Of c2) 'err Error    1    Type argument 'c2' does
not inherit from or implement the constraint type 'b(Of a)'.

        End Class
        Public Class b(Of T As a)

        End Class

        Public Class c
            Inherits b(Of a)

        End Class
        Public Class c1
            Inherits b(Of a)

        End Class
        Public Class c2
            Inherits b(Of a1)

        End Class
        Public Class c3
            Inherits b(Of a2)

        End Class
        Public Class d(Of T As b(Of a))

        End Class
        Dim r As New d(Of c3) 'err Error    1    Type argument 'c2' does not
inherit from or implement the constraint type 'b(Of a)'.

        Dim r1 As New d(Of c) 'ok

    End Class

15 May 2009 12:21 AM

Family Tree Mike

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"×“× ×™" <da***@si-eng.co.il> wrote in message
news:A3BDBD85-A500-4391-BC4A-1025AE2FDA94@microsoft.com...
>   Public Class Form1
>        Public Class a
>
>        End Class
>        Public Class a1
>            Inherits a
>        End Class
>        Public Class a2
>            Inherits a
>            Private dsfs As d(Of c2) 'err Error 1 Type argument 'c2' does
> not inherit from or implement the constraint type 'b(Of a)'.
>
>        End Class
>        Public Class b(Of T As a)
>
>        End Class
>
>        Public Class c
>            Inherits b(Of a)
>
>        End Class
>        Public Class c1
>            Inherits b(Of a)
>
>        End Class
>        Public Class c2
>            Inherits b(Of a1)
>
>        End Class
>        Public Class c3
>            Inherits b(Of a2)
>
>        End Class
>        Public Class d(Of T As b(Of a))
>
>        End Class
>        Dim r As New d(Of c3) 'err Error 1 Type argument 'c2' does not
> inherit from or implement the constraint type 'b(Of a)'.
>
>        Dim r1 As New d(Of c) 'ok
>
>    End Class

Converting this to something real world:

Public Class Animal ' was class a
End Class

Public Class Mammal ' was class a1
    Inherits Animal
End Class

Public Class Reptile ' was class a2
    Inherits Animal
    Private dsfs As ZooAssociation(Of SmallMammalZoo) ' fails
    Private dsfsCorrect As ZooAssociation(Of Zoo(Of Animal)) ' works
End Class

Public Class Zoo(Of T As Animal) ' was class b(of a)
End Class

Public Class PettingZoo ' was class c
    Inherits Zoo(Of Animal)
End Class

Public Class Farm ' was class c1
    Inherits Zoo(Of Animal)
End Class

Public Class SmallMammalZoo ' was class c2
    Inherits Zoo(Of Mammal)
End Class

Public Class ReptileZoo ' was class c3
    Inherits Zoo(Of Reptile)
End Class

Public Class ZooAssociation(Of T As Zoo(Of Animal)) ' was class d
End Class

Module Module1
    Sub Main()
        Dim r As New ZooAssociation(Of ReptileZoo) ' fails
        Dim rCorrect As New ZooAssociation(Of Zoo(Of Animal)) ' works
    End Sub
End Module

In both cases, you are trying to use a restrictive zoo (SmallMammalZoo and
ReptileZoo), where Zoo(of Animal) is required. A Zoo(of Animal) can contain
both SmallMammal objects and Reptile objects. Since a ZooAssociation object
can have a more generic Zoo added to it, you would have problems reading
through it when you stumbled onto an Octopus :-)

I hope this helps.

--
Mike

15 May 2009 6:50 AM

×“× ×™

thanke ypu for your answer.
i want to creat a class that get zoo animel and work with animel properties
such as name or coloul of the animel. how can i do it?
Public Class Animal ' was class a

End Class

Public Class Mammal ' was class a1
     Inherits Animal
End Class

Public Class Reptile ' was class a2
     Inherits Animal
     Private dsfs As ZooAssociation(Of SmallMammalZoo) ' fails
     Private dsfsCorrect As ZooAssociation(Of Zoo(Of Animal)) ' works
End Class

Public Class Zoo(Of T As Animal) ' was class b(of a)
End Class

Public Class PettingZoo ' was class c
     Inherits Zoo(Of Animal)
End Class

Public Class Farm ' was class c1
     Inherits Zoo(Of Animal)
End Class

Public Class SmallMammalZoo ' was class c2
     Inherits Zoo(Of Mammal)
End Class

Public Class ReptileZoo ' was class c3
     Inherits Zoo(Of Reptile)
End Class
Public Class ZooAssociation(Of T As Zoo(Of Animal)) ' was class d
End Class

Module Module1
    Sub Main()
         Dim r As New ZooAssociation(Of ReptileZoo) ' fails
         Dim rCorrect As New ZooAssociation(Of Zoo(Of Animal)) ' works
     End Sub
End Module

Show quoteHide quote

"Family Tree Mike" wrote:

> "×“× ×™" <da***@si-eng.co.il> wrote in message
> news:A3BDBD85-A500-4391-BC4A-1025AE2FDA94@microsoft.com...
> >   Public Class Form1
> >        Public Class a
> >
> >        End Class
> >        Public Class a1
> >            Inherits a
> >        End Class
> >        Public Class a2
> >            Inherits a
> >            Private dsfs As d(Of c2) 'err Error 1 Type argument 'c2' does
> > not inherit from or implement the constraint type 'b(Of a)'.
> >
> >        End Class
> >        Public Class b(Of T As a)
> >
> >        End Class
> >
> >        Public Class c
> >            Inherits b(Of a)
> >
> >        End Class
> >        Public Class c1
> >            Inherits b(Of a)
> >
> >        End Class
> >        Public Class c2
> >            Inherits b(Of a1)
> >
> >        End Class
> >        Public Class c3
> >            Inherits b(Of a2)
> >
> >        End Class
> >        Public Class d(Of T As b(Of a))
> >
> >        End Class
> >        Dim r As New d(Of c3) 'err Error 1 Type argument 'c2' does not
> > inherit from or implement the constraint type 'b(Of a)'.
> >
> >        Dim r1 As New d(Of c) 'ok
> >
> >    End Class
>
>
> Converting this to something real world:
>
> Public Class Animal ' was class a
> End Class
>
> Public Class Mammal ' was class a1
>     Inherits Animal
> End Class
>
> Public Class Reptile ' was class a2
>     Inherits Animal
>     Private dsfs As ZooAssociation(Of SmallMammalZoo) ' fails
>     Private dsfsCorrect As ZooAssociation(Of Zoo(Of Animal)) ' works
> End Class
>
> Public Class Zoo(Of T As Animal) ' was class b(of a)
> End Class
>
> Public Class PettingZoo ' was class c
>     Inherits Zoo(Of Animal)
> End Class
>
> Public Class Farm ' was class c1
>     Inherits Zoo(Of Animal)
> End Class
>
> Public Class SmallMammalZoo ' was class c2
>     Inherits Zoo(Of Mammal)
> End Class
>
> Public Class ReptileZoo ' was class c3
>     Inherits Zoo(Of Reptile)
> End Class
>
> Public Class ZooAssociation(Of T As Zoo(Of Animal)) ' was class d
> End Class
>
> Module Module1
>     Sub Main()
>         Dim r As New ZooAssociation(Of ReptileZoo) ' fails
>         Dim rCorrect As New ZooAssociation(Of Zoo(Of Animal)) ' works
>     End Sub
> End Module
>
>
> In both cases, you are trying to use a restrictive zoo (SmallMammalZoo and
> ReptileZoo), where Zoo(of Animal) is required. A Zoo(of Animal) can contain
> both SmallMammal objects and Reptile objects. Since a ZooAssociation object
> can have a more generic Zoo added to it, you would have problems reading
> through it when you stumbled onto an Octopus :-)
>
> I hope this helps.
> --
> Mike
>

15 May 2009 12:56 PM

Family Tree Mike

"×“× ×™" wrote:

> thanke ypu for your answer.
> i want to creat a class that get zoo animel and work with animel properties
> such as name or coloul of the animel. how can i do it?

It would seem that:

dim MyPets = new List(of Animal)

would be sufficient. I have a feeling that something is beling lost in
translation somewhere.

Mike