Proto for Boost mailing list page: Re: [proto] Hold terminals by "smart" reference

Subject: Re: [proto] Hold terminals by "smart" reference
From: Eric Niebler (eric_at_[hidden])
Date: 2012-06-03 12:36:36

On 6/3/2012 6:23 AM, Mathias Gaunard wrote:
> On 03/06/2012 02:59, Eric Niebler wrote:
> 
>> There is no way to hook proto::value to return anything but what is
>> stored in the terminal. It's a very dumb, low-level function. You could
>> easily define your own value function that does something smarter, tho.
> 
> I'm currently doing it with my own function, but that means I need to
> use my own value instead of Proto's everywhere (value, result_of::value,
> or _value).

Right.

> Plus I don't have a good way to distinguish between a terminal of
> shared_ptr<T> and a terminal of T which is held through a shared_ptr.

Have you tried a grammar? Something like (untested) proto::terminal<
boost::shared_ptr< proto::_ > > ?

> I was considering specializing something like expr<Tag,
> term_shared<Arg>, 0> and basic_expr<Tag, term_shared<Arg>, 0> to do
> this, but it appears I also need to change proto::value itself to call a
> function instead of returning child0 directly.

In my opinion, defining your own value function would be a much easier,
cleaner solution.

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com