Inheritence - Create derived class from base class...options???

Thanks for the attempt, but this is not what I am looking for.  From my original post:  

"If I have a Class Animal, is there any way to "convert" it to Monkey without copying over all of the properties?"

Copying over the individual properties can get very cumbersome, and will cause me to go back into the derived classes and update them all individually each time a property is added to the base class.  

Because the base class is part of the derived class, I was hoping there was a way to tell .Net to create the derived class, using the base class (and keep the existing data).

Have yout tried something like

myMonkey = CType(myAnimal, Monkey)

or

myMonkey = DirectCast(myAnimal, Monkey)

myPet = CType(myPet , Monkey)

or

myPet = DirectCast(myPet , Monkey)

I guess that is not it either

I think Roland was on the right track...all you need to do is add a little REFLECTION magic and it will be completely generic and not need to be updated as you add/remove fields:

Public Class Form1
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim myPet As New Animal
        myPet.Legs = 2
        myPet.Name = "Sparky"
 
        Dim myMonkey As New Monkey(myPet)
        myMonkey.HasTail = True
        Debug.Print("myMonkey.Legs = " & myMonkey.Legs)
        Debug.Print("myMonkey.Name = " & myMonkey.Name)
        Debug.Print("myMonkey.HasTail = " & myMonkey.HasTail)
    End Sub
 
End Class
 
Public Class Animal
 
    Public Name As String
    Public Legs As Int16
 
End Class
 
Public Class Monkey
    Inherits Animal
 
    Public Sub New()
    End Sub
 
    Public Sub New(ByVal DeriveFrom As Animal)
        For Each fi As System.Reflection.FieldInfo In DeriveFrom.GetType.GetFields(Reflection.BindingFlags.Instance Or Reflection.BindingFlags.Public Or Reflection.BindingFlags.NonPublic)
            Dim fi2 As System.Reflection.FieldInfo = Me.GetType.GetField(fi.Name, Reflection.BindingFlags.Instance Or Reflection.BindingFlags.Public Or Reflection.BindingFlags.NonPublic)
            If Not IsNothing(fi2) Then
                fi2.SetValue(Me, fi.GetValue(DeriveFrom))
            End If
        Next
    End Sub
 
    Public HasTail As Boolean
 
End Class
                                              

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I know that not all Animals are Monkeys...  But all Monkeys have the base properties and functions of Animals, so I don't want to have to create a whole new Monkey...  And I don't want to have to care about what additional properties a monkey has, because all I want to do is get a new Monkey that uses my initiated Animal as it's base - but without copying properties (at least not individually)...

The best way I have come up with so far is to use serialization to serialize Animal, change it's serialized type to Monkey, then deserialize it.  The attached code file does this.

It does have a problem, as it will obviously have overhead in the conversion process - but I don't need to know anything about either object to do this - as long as they are "serializable".  

So, I can convert a base object into any object that it derives to with a simple function call.
 - If the base object changes, all new properties and fields get copied automatically (as defined by the serialization of the object).

So, the only outstanding question I have...

Can you achieve this without serialization/deserailization?

    Public Class Convert
        Public Shared Function ToDerivedType(Of pDerivedType)(ByRef pBase As Object) As pDerivedType
            Dim myWriter As New IO.StringWriter
            Dim oXSBase As XmlSerializer = New XmlSerializer(pBase.GetType())
            oXSBase.Serialize(myWriter, pBase)
 
            Dim myNewData As String = myWriter.ToString()
            myNewData = Replace(myNewData, "<" & pBase.GetType().Name & " xmlns", "<" & GetType(pDerivedType).Name & " xmlns")
            myNewData = Replace(myNewData, "</" & pBase.GetType().Name & ">", "</" & GetType(pDerivedType).Name & ">")
 
            Dim myReader As New IO.StringReader(myNewData)
            Dim oXSDerived As XmlSerializer = New XmlSerializer(GetType(pDerivedType))
            Return oXSDerived.Deserialize(myReader)
        End Function
    End Class
                                              

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PS.  Test code to do this is:

    <Serializable()> _
    Public Class Animal
        Public Name As String
        Public Legs As Int16
        Public Overrides Function ToString() As String
            Return Name & " has " & Legs & " legs"
        End Function
    End Class
 
    <Serializable()> _
    Public Class Monkey
        Inherits Animal
        Public ReadOnly Property HasTail() As Boolean
            Get
                Return True
            End Get
        End Property
        Public Overrides Function ToString() As String
            Return MyBase.ToString() & IIf(HasTail, " and a", " but no") & " tail!"
        End Function
    End Class
 
 
Public Sub Test()
    Dim myAnimal As New Simple.Animal
    myAnimal.Name = "Bingo"
    myAnimal.Legs = 2
    MessageBox.Show(myAnimal.ToString())
 
    Dim myMonkey As Simple.Monkey = Simple.Convert.ToDerivedType(Of Simple.Monkey)(myAnimal)
    MessageBox.Show(myMonkey.ToString())
End Sub

                                              

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"...all I want to do is get a new Monkey that uses my initiated Animal as it's base - but without copying properties (at least not individually)..."

Did you not see my post?...it copies everyhing via Reflection.  It will work even when you change the base class fields...

And sorry, but yes - I tried all of the following:

dim myMonkey as Monkey = myAnimal
dim myMonkey as Monkey = CType(myAnimal, Monkey)
dim myMonkey as Monkey = DirectCast(myAnimal, Monkey)

I've even tried to add a New Constructor in Monkey that accepts an object of type Animal and set MyBase = pAnimal, but it's not allowed.  This would be the best solution, as that is EXACTLY what I want to do.  Create a monkey and pass the base object into the New Constructor to override MyBase...

It just does not seem to be possible.

Idle_Mind

Your solution would work in a simple example, but I'm trying to avoid copying the properties.  I know that using reflection is possible, but I have read that it cannot always be done in complex objects (as the real world will have).  

Regardless of your solution or mine, which both work - I'm trying to do it without copying anything.  The base object exists.  I should be able to create a New derived object from it - but I can't figure it out.

I think you're right Idle_Mind...  

If I understand it right, I can use the Binary Formatter instead of the XmlSerialization, and it will keep the object in binary form - and thus speed up the "conversion process"...  

Then, essentially, I'll be doing exactly what I want - which is creating a new monkey with existing animal, without re-initializing animal, right?

It should work...though I don't really know if it's any faster.  You'll have to test it... ;)

Upcasting (or downcasting - not sure if I have them flipped) is not possible.  

I guess at this point the only question to ask is 'why'.   Why do you need to do this?  In the case of most base classes like this, Animal should conceptually be abstract.  There is no such animal as 'animal' so consequently constructing such a type shouldn't be allowed.  

Why can't  you use reflection?  

Why can't you use a factory pattern to create the correct type and cast it down to animal?

Why can't you use serialization?

And I've been here before so I understand what it's like to be on the other end of this question, but why are you so hell-bent on making the compiler do something for you that you already have a handful of ways to do yourself?

b_levitt

I'm trying to encapsulate logic, functionality, etc inside of an object that is NOT exposed outside of my business layer.  I want the business layer to just "see" an animal.  It doesn't need to know what kind of animal it is - it just needs to know it's an animal.

However, when that animal object is back to the business layer, it actually IS A monkey, and the business layer knows this - and therefore uses the hidden functionality allowed in the business layer because the BL can tell it's not just an animal, but a monkey.

This keeps the presentation of the object outside the business layer very simple, but also allows the business layer to have full access.

So, I want the presentation layer to be able to pass the business layer an Animal (by reference).  When the BL sees the object is an animal, it will convert it to a monkey and set the reference to point to the monkey instead.  But, the PL doesn't know the difference because it's still inhereted from Animal.

The BL has full access to everything that it needs.
The PL doesn't even know the difference.

I'm trying to enforce separation of logic and complexity in the layers so that one layer doesn't even see what it doesn't need to know.

In paragraph 1 above, I mean:

"I want the presentation layer to just "see" an animal.  It doesn't need to know what kind of animal it is - it just needs to know it's an animal."

You could consider implementing an Animal INTERFACE instead of deriving from a Base Class.  Then the PL just gets pass something the implements the Interface and can perform the "base operations" on that object regardless of what it actually is.

Not to derail, but I know in C# you can refer to everything as the base type "object" and if you perform an "IS" comparison you can determine what class it really is (or part of).

Therefore you could have arrays of Animals, and refer to them as such, but if you could also go through and find which ones are monkeys.   Does VB not have that same capability?

example being
Dim X as Animal
X = new Monkey()

Though because X is referred to as Animal only those parameters are visible.
however if you have a function that accepts Monkeys this one would be a valid item.
Or does that not work in VB?

The "solution" was never found for what I want to do - but several alternatives were discussed.

Tribmos, that actually looks like what I'm trying to do...  

Dim X as Animal
X.Name = "Bingo"
X = new Monkey()

But in VB, when you say X = new Monkey, it will create a New instance of Monkey from scratch and it will have no instantiated properties of the previously instantiated Animal...  

What I'd like to do is keep X.Name populated and use X to create an instance of Monkey.  

Idle

BTW - I wrote the Class Converter utility using reflection (as you suggested) and it is much faster than doing it my way (converting using serialization).  

However, I did run across a problem.  The copy using reflection logic does not work on private member variables of the base type.  It finds them on the base type when it's looping through, but can't see them on the derived type (because they're private on the base, and not exposed in the derived object).