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Re: GC and multiple inheritance as in C++

by Jason Whittington :: Rate this Message:

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I believe the answer here is: “no”. MI languages have to find a way to fake it.

Microsoft’s C++/CLI fakes it by not allowing MI for managed types. MI classes are represented as value types in the CLI and thus don’t behave with “true” polymorphism. They do in the sense that C++ code compiled together works correctly, but to other languages the inheritance is opaque – calling GetType().BaseType will just yield System.ValueType.

The CLR port of Eiffel fakes it by using a [somewhat complex and arcane] scheme where inheritance in Eiffel is modeled with interfaces in .NET.

Jason

From: mono-gc-list-bounces@... [mailto:mono-gc-list-bounces@...] On Behalf Of Juro Jon
Sent: Thursday, June 12, 2008 8:36 PM
To: mono-gc-list@...
Subject: Re: [Mono-gc-list] GC and multiple inheritance as in C++

I don't know much of CLI specification so I may be missing something trivial. Java GC assumes that all pointers point to some "header" to identity the memory object. Since Java is single inheritance a pointer always points to the head of a full object, but for C++ multiple inheritance it may be pointing to an embedded part and need to be adjusted to find the full object. Are you saying that the CLI GC or typesystem has some way to do this adjustment?

Thanks

On Fri, Jun 13, 2008 at 3:50 AM, David Jeske <jeske@...> wrote:

AFAIK, you don't need C++ MI to have a pointer to something inside an object
body. This can happen if you take a ref of any instance data in C#.

http://www.java2s.com/Code/CSharp/Language-Basics/CRefandOutParameters.htm

-- Juro Jon wrote:
> Hello, I have a question concerning implementation of multiple inheritance in
> CIL. For a C++ MI object, a pointer can points to inside the object body
> instead of the its head. eg.
> struct A : B, C { }; C* c = new A;
> While Boehm GC detects this kind of reference, is it a supported feature of
> Mono? If not, what is the suggested way to implement it (eg. what is the
> C++/CLI way) ?

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