Re: flyweight object equivalence

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Tue, 17 Apr 2007 17:24:19 -0400

Message-ID:

<#OLzieTgHHA.4708@TK2MSFTNGP04.phx.gbl>

Jason S <jmsachs@gmail.com> wrote:

Hmm. After embracing the idea of flyweights (multiple small COM
objects used to access/represent a common underlying shared object)
I'm running up against a subtlety, namely I am not sure how to provide
the functionality for testing equality.

If I wanted to compare this information in C++, it's easy; I just
compare these 2 items with their appropriate operator ==() methods.

But how do I compare flyweights for equivalence in COM?

Well, if it's meaningful for your COM objects to be tested for equality,
you would have to provide an Equals method on one of the interfaces they
implement. Just like you provide operator== method on your C++ objects.

I'm not even sure what method
to provide in an IDL file to allow objects to be compared.

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

It's just an example. The method doesn't have to be named Equals, and
doesn't have to have this exact signature. There is no standard for such
a method, you are free to design whatever makes sense.
--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925