Re: template classes: inheritance problem

From:

Ulrich Eckhardt <eckhardt@satorlaser.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 6 Feb 2009 12:33:38 CST

Message-ID:

<u0tt56-djk.ln1@satorlaser.homedns.org>

vl106 wrote:

I think templates are a good solution to my problem:
[PSEUDOCODE]
void receive_message(int messageId, char* messageData) {
Base& newMessage = Factory::create(messageId, messageData);
newMessage.process();
}

The receive_message function will stay pretty stable. If new kind of
message is "invented" only a new specialication has to be created.

What really differs is the process method. Each specialization (based
on messageId) has ist own (and different) behaviour.

struct base {
   virtual ~base();
   virtual void process() = 0;
};

template<int n>
struct common: base {
   ...
};

struct message1: common<1> {
   virtual void process() { ... }
};

Whether the 'common' class makes sense or not depends on your design. I
could also imagine a non-template class that simply takes the '1' as
parameter. Note that you can also derive from multiple base classes, which
can be used for so-called 'mixins' (do a websearch!) that encapsulate some
common functionality. Another thing worth looking at could be CRTP.

Uli

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