Current Cast vs. Object Type

I am trying to determine what the current cast of an object is.
Essentially, if I use GetType, it always returns the original type
of the object created but I want to know what the current cast of
the object is (i.e.: is it still cast as a Derived class, or is it
cast as a Base class?) Here is some pseudo code to show the example.
>
Class Base
>
...
End Class
>
Class Derived : Inherits Base
>
...
End Class
>
Public Sub Main()
Dim derived1 as New Derived()
Dim base1 as Base
>
base1 = Ctype(derived1, Base)
>
Console.Writeline (base1.GetType().ToString())
>
End Sub
>
'Output would be "Derived". How to I determine what the CAST is?
i.e. Base?
>
Thanks in advance.
>
Dinsdale

>I am trying to determine what the current cast of an object is.
Essentially, if I use GetType, it always returns the original type of
the object created but I want to know what the current cast of the
object is (i.e.: is it still cast as a Derived class, or is it cast as
a Base class?) Here is some pseudo code to show the example.
>
Class Base
>
...
End Class
>
Class Derived : Inherits Base
>
...
End Class
>
Public Sub Main()
Dim derived1 as New Derived()
Dim base1 as Base
>
base1 = Ctype(derived1, Base)
>
Console.Writeline (base1.GetType().ToString())
>
End Sub
>
'Output would be "Derived". How to I determine what the CAST is? i.e.
Base?
>
Thanks in advance.
>
Dinsdale
>

"Dinsdale" <russ.ha...@gmail.comschrieb
>
>
>>>>>>>>>>>>>
Why would you want to know this? The compiler permits what's possible with
the reference anyway. I don't dare to say "look at the dim statement" ;-)
>
With local variables this is not possible. With fields, you could use
reflection (whyever) and have a look at System.Type.DeclaringType.
>
Armin

What are you trying to do ? You could get the base type or an ancestor type
using Reflection.
>
Strictly speaking you can't do that as once you casted the variable to
another variable you don't have any information about where it came from.
Basically this is bit as if you wanted to know if an integer variable was
created from a constant in the code or parsed from a string or taken from
another variable etc....
>
IMO the first step would be to explain what you are trying to do so that we
can understand if reflection would be enough or if someone can suggest
another way of doing whatever you are trying to do.
>
---
Patrice
>
"Dinsdale" <russ.ha...@gmail.coma écrit dans le message de news:
1183043084.135466.165...@n60g2000hse.googlegroups. com...
>>>>>>>>>>>>

On Jun 28, 10:35 am, "Armin Zingler" <az.nos...@freenet.dewrote:>
Ya, I was waiting for someone to say that. lol.
>
The database uses a sequence number for all primary keys in the
table and we are trying to create a class library around it. I
didn't want to have to code derived classes as having base_id,
derived_id,
derived_2_id so I've created a collection of identifiers (including
concurrency identifiers such as modified date). Then the lowest base
class has an ID property that looks at the type and returns the
correct Identifier value from the collection for that cast. The
problem is GetType() doesn't do this, as noted above. The following
is the code that doesn't work. :(
>
Public Property ID() As Integer
Get
CheckIdentifiers() 'Ensures that there are in fact identifiers
Dim typeName As String
typeName = Me.GetType.Name
Return Identifiers(typeName).ID
End Get
Set(ByVal value As Integer)
CheckIdentifiers()
Dim typeName As String
typeName = Me.GetType.Name
Identifiers(typeName).ID = value
End Set
End Property
>
>
So, If I create an object of DerivedType2 and want to cast it as a
BaseType and then get the BaseType.ID property, the above code
executes as DerivedType2 so I get the wrong ID.
>
Unfortunately, in my test app the DeclaringType is coming up as
Nothing, but thanks for the help. It gives me something to work
on...

On Jun 28, 10:35 am, "Armin Zingler" <az.nos...@freenet.dewrote:>
Ya, I was waiting for someone to say that. lol.
>
The database uses a sequence number for all primary keys in the table
and we are trying to create a class library around it. I didn't want
to have to code derived classes as having base_id, derived_id,
derived_2_id so I've created a collection of identifiers (including
concurrency identifiers such as modified date). Then the lowest base
class has an ID property that looks at the type and returns the
correct Identifier value from the collection for that cast. The
problem is GetType() doesn't do this, as noted above. The following is
the code that doesn't work. :(
>
Public Property ID() As Integer
Get
CheckIdentifiers() 'Ensures that there are in fact identifiers
Dim typeName As String
typeName = Me.GetType.Name
Return Identifiers(typeName).ID
End Get
Set(ByVal value As Integer)
CheckIdentifiers()
Dim typeName As String
typeName = Me.GetType.Name
Identifiers(typeName).ID = value
End Set
End Property
>
>
So, If I create an object of DerivedType2 and want to cast it as a
BaseType and then get the BaseType.ID property, the above code
executes as DerivedType2 so I get the wrong ID.
>
Unfortunately, in my test app the DeclaringType is coming up as
Nothing, but thanks for the help. It gives me something to work on...
>
Cheers
Dinsdale
>
>

The database uses a sequence number for all primary keys in the table
and we are trying to create a class library around it. I didn't want
to have to code derived classes as having base_id, derived_id,
derived_2_id so I've created a collection of identifiers (including
concurrency identifiers such as modified date). Then the lowest base
class has an ID property that looks at the type and returns the
correct Identifier value from the collection for that cast.

Dinsdale wrote:>
/If/ I understand this correctly, you want each derived class to be able
to change the value of the ID that it works with?
>
That's a job for Overriding.
>
Class Base
Public Overridable ReadOnly Property ID() as Integer
Get
Return m_iSomeIdentifier
End Get
End Property
End Class
>
Class Derived
Inherits Base
Public Overrides ReadOnly Property ID() As Integer
Get
Return m_iOtherIdentifier
End Get
End Property
End Class
>
Now, it doesn't matter what type of variable you put either of the above
into; each works out which Identifier it needs to work with.
>
(/If/ I understand this correctly ...)
>
HTH,
Phill W.

On Jul 2, 7:22 am, "Phill W." <p-.-a-.-w-a-r...@-o-p-e-n-.-a-c-.-u-k>
wrote:
>
>
>>>>>>>>>
Phill,
>
Yes, your understanding is correct (thank you, I didn't want to have
to re-type my original posting!). Unfortunately, I do not get the
results that I was anticipating. regardless of the current cast of the
object, I still get the value from the property of the original
declaring type. Maybe I'm doing something wrong (I hope)?
>
Module Module1
Public MustInherit Class BaseClass
>
Public MustOverride Property ID() As Integer
>
End Class
>
Public Class Derived1
Inherits BaseClass
>
Private _derived1Int As Integer
Public Overrides Property ID() As Integer
Get
Return _derived1Int
End Get
Set(ByVal value As Integer)
_derived1Int = value
End Set
End Property
>
Public Sub New(ByVal der1 As Integer)
_derived1Int = der1
End Sub
>
End Class
>
Public Class Derived2
Inherits Derived1
>
Private _derived2Int As Integer
Public Overrides Property ID() As Integer
Get
Return _derived2Int
End Get
Set(ByVal value As Integer)
_derived2Int = value
End Set
End Property
>
Public Sub New(ByVal der1 As Integer, ByVal der2 As Integer)
MyBase.New(der1)
_derived2Int = der2
End Sub
End Class
>
Sub Main()
Dim der2 As New Derived2(12, 3)
>
Console.WriteLine("The ID from the Derived2 object pointer is: {0}",
der2.ID)
>
Dim der1 As Derived1
>
der1 = CType(der2, Derived1) 'The CType call is just for the sake of
being explicit...
>
Console.WriteLine("The ID from the Derived1 object pointer is: {0}",
der1.ID)
>
Console.Read()
End Sub
>
End Module
>
Any suggestions?
>
Thanks for all the help!
>
Dinsdale

On Jul 3, 10:06 am, Dinsdale <russ.ha...@gmail.comwrote:
>
>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Oh, I guess I should post the results and what I expect? lol.
>
What I was HOPING to get was:
>
The ID from the Derived2 Object Pointer is: 3
The ID from the Derived1 Object Pointer is: 12
>
The ACTUAL output was as follows:
>
The ID from the Derived2 Object Pointer is: 3
The ID from the Derived1 Object Pointer is: 3
>
Cheers
Dinsdale

On Jul 3, 10:13 am, Dinsdale <russ.ha...@gmail.comwrote:
>
>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Ha ha! One of my work mates seems to have solved the problem. The
solution is to use the Shadows keyword. I'll post the explicit
implementation when I figure out how I want to do it...
>
Thanks everyone!
Dinsdale