Re: template problem: local variable as non-type argument

From:
Anthony Williams <anthony.ajw@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Fri, 6 Feb 2009 12:33:18 CST
Message-ID:
<87d4dv65cg.fsf@dell.justsoftwaresolutions.co.uk>
vl106 <vl106@hotmail.com> writes:

I have to better describe the problem:

[kind of pseudo code]
void receive_message(int messageId, char* data) {
    Base& new_message = Factory::createMessage(messageId, data); //
transition to C++
    new_message.process();
}

From old, non-C++ library I receive messages identified by int id.

I want to map this "event" into an "object-oriented" message. Further
receive_message should stay stable. That is when a new kind of message
is received I only want to create a new specialization
(C<new_message_id>).
This specialization will have a process method with different
behaviour.


Why do you need a specialization? Why can't you just define a normal
class derived from Base? Once you're out of createMessage you can't
access the derived class anyway unless you know what it is.

I would just have createMessage do a lookup of ID to class to create,
either using a switch statement or a lookup table.

Anthony
--
Author of C++ Concurrency in Action | http://www.manning.com/williams
just::thread C++0x thread library | http://www.stdthread.co.uk
Just Software Solutions Ltd | http://www.justsoftwaresolutions.co.uk
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