Re: flyweight object equivalence

From:
"Alexander Nickolov" <agnickolov@mvps.org>
Newsgroups:
microsoft.public.vc.atl
Date:
Wed, 18 Apr 2007 12:11:01 -0700
Message-ID:
<uZjuO1egHHA.1388@TK2MSFTNGP05.phx.gbl>
Well, it also fails if the two objects are from the same in-proc
server, but in different apartments. Then again, this may actually
be desired behavior...

--
=====================================
Alexander Nickolov
Microsoft MVP [VC], MCSD
email: agnickolov@mvps.org
MVP VC FAQ: http://vcfaq.mvps.org
=====================================

"Igor Tandetnik" <itandetnik@mvps.org> wrote in message
news:edA92%23TgHHA.1388@TK2MSFTNGP05.phx.gbl...

Jason S <jmsachs@gmail.com> wrote:

On Apr 17, 5:24 pm, "Igor Tandetnik" <itandet...@mvps.org> wrote:

HRESULT Equals([in] IMyInterface* other, [out, retval] VARIANT_BOOL
ret);


sure, this is an obvious choice for interface. But the implementation
seems far from obvious, since the two objects can't talk to each other
in C++


I suggest implementing a private interface alongside IMyInterface. Mark it
[local] in the IDL. A method on this interface can even return a raw C++
pointer to the object, e.g. as a void* pointer.

A variation of this technique goes like this:

class CMyComObject {
BEGIN_COM_MAP(CMyComObject)
   // ...
   COM_INTERFACE_ENTRY_IID(GUID_INTERNAL, CMyComObject)
END_COM_MAP()
};

GUID_INTERNAL is a new GUID you define in your C++ files and never mention
in any IDL. QueryInterface for this GUID only works within the same
apartment, and produces a raw C++ pointer to the underlying object. If the
QI call fails, then either this instance comes from a different server, or
it's somebody else's implementation of IMyInterface. In either case, you
can simply declare the two objects to not be equal.
--
With best wishes,
   Igor Tandetnik

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