Generics and inheritance

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Sorry if this is the wrong group, but I cna think not of where else to post.

I have an inheritance hierarchy in place as follows ...

PersonVisitor<T<-- AlphabeticVisitor<T<-- FamilyNameVisitor<T>

public interface IPerson
{
string GivenName { get; set; }
string FamilyName { get; set; }
IPerson Clone();
void Visit(PersonVisitor<IPersonvisitor);
}

public abstract class PersonVisitor<Twhere T : IPerson
{
virtual public void Visit(T c) { }
}

public abstract class AlphabeticVisitor<T: PersonVisitor<Twhere T :
IPerson
{
// class code omited
}

public class FamilyNameVisitor<T: AlphabeticVisitor<Twhere T : IPerson
{
override public void Visit(T c)
{
}
}

Firstly, I would expect that I could pass an object of type
FamilyNameVisitor<Tas follows

Customer c = PeopleFactory.CreateNewCustomer("Marcus", "Barnard");
Assert.IsNotNull(c, "Failed to instantiate the Customer object");
FamilyNameVisitor<Customerv = new FamilyNameVisitor<Customer>();
c.Visit(v);

However, I am told that this is not possible because an object of type
FamilyNameVisitor<Customercannot be converted to type
PersonVisitor<IPerson(even though FamilyNameVisitor<Customeris a
sub-class of PersonVisitor<IPerson>, AND Customer is a sub-class of IPerson)

So, I then put the following implicit conversion into the FamilyNameVisitor
class definition

public static implicit operator
PersonVisitor<IPerson>(FamilyNameVisitor<Tv)
{
return (v as PersonVisitor<IPerson>);
}

but this conversion always returns null :o(

Can somebody please help?

Thanks in advance

--
Of all words of tongue and pen, the saddest are: "It might have been"

Bill.Richards @ greyskin .co .uk
http://greyskin.co.uk

[Mattias Sjögren]

>However, I am told that this is not possible because an object of type

>FamilyNameVisitor<Customercannot be converted to type
PersonVisitor<IPerson(even though FamilyNameVisitor<Customeris a
sub-class of PersonVisitor<IPerson>, AND Customer is a sub-class of IPerson)

FamilyNameVisitor<Customeris *not* a subclass of
PersonVisitor<IPerson>. In your case I think the easiest solution is
to make the Visit method generic as well

void Visit<T>(PersonVisitor<Tvisitor) where T : IPerson
Mattias

--
Mattias Sjögren [C# MVP] mattias @ mvps.org
http://www.msjogren.net/dotnet/ | http://www.dotnetinterop.com
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