Re: [boost] boost::proto short example

From: Maurizio Vitale (maurizio.vitale_at_[hidden])
Date: 2007-04-16 05:45:00

Eric Niebler <eric_at_[hidden]> writes:

>> I hope Eric can find the time to review it and maybe add it to the boost::proto
>> examples. I would certainly have benefited from something like this being available.
>> On the other hand, I've learned more by doing it. Thanks to Eric for
>> having helped me and for making boost::proto available.
>
> <snip code>
>
> I have no comments about your use of proto -- it looks a lot like the 
> lazy_vector example from the users' guide, in fact.

Another difference, again probably obvious to the seasoned user, but
that the average newcomer might miss is that in order to allow an
assignment of the form:

   int v = ...expr involving extended types...

you seem to need an operator int () in the wrapping expression. That
was the best I managed to do and the only reason I needed to wrap
boost::proto expressions in my example.  If there's a better way, I'd
like to know.

The lazy vector example doesn't show anything of sort. The nearest is
the line:

    double d1 = (v1 + v2)[2]

but there the double comes from the evaluation of operator[].

I still think that an example on lightweight DSLs, where you're not
drastically change domain, but what you need is almost plain C++
expression would be useful.

The example I posted shows how to wrap a UDT and how to slightly
modify the semantics of a few operators.

The next example I'm working on will show how to define multiple
version of these and control what can be mixed with what (and
furthemore define the type of the result when they mix together).

Again, small things, but having a cookbook of these may be very
helpful to newcomers to proto.  I think that the effort it takes to
people to understand concepts can be minimized by moving from the
territory they know up in reasonably small steps.

A big-bang example showing the mighty of proto is very good for
catching the attention and convincing people that investing time in
proto is worthwhile, but then it is important not to lose them off the
learning curve.

I'll keep posting what I'm learning with your help. I hope boost.devel
is the right place, as boost::proto has not been officially included
in boost yet and this is probably where early adopters hang around.

     Maurizio