Proto for Boost mailing list page: Re: [proto] Can't use template domain class with BOOST_PROTO_BASIC_EXTENDS

Subject: Re: [proto] Can't use template domain class with BOOST_PROTO_BASIC_EXTENDS
From: Eric Niebler (eric_at_[hidden])
Date: 2010-10-09 15:15:21

On 10/9/2010 12:02 PM, joel falcou wrote:
> Trying to use template domain class with BOOST_PROTO_BASIC_EXTENDS
> ends up in an error leading to the fact this ligne in the macro is
> incorrect when the Domain is template:
> 
>     BOOST_PROTO_BASIC_EXTENDS_(Expr, Derived, Domain)
>     typedef void proto_is_aggregate_;
>     typedef Domain::proto_generator proto_generator;
> 
> Obviously this is alckign a typename before Domain::proto_generator if
> Domain is actually a template class.

You mean, if Domain is a template parameter. Crap.

> Thing is used to work before ( aorund 1.40) so I guess somethign changed
> around here.
> I guess a details meta-function extracting the domain will fix that or
> am I wrong ?
> 
> namespace boost { namespace proto
> {
>   template<class Domain> generator_of
>   {
>       typedef typename Domain::proto_generator type;
>   };
> } }
> 
>     BOOST_PROTO_BASIC_EXTENDS_(Expr, Derived, Domain)
>     typedef void proto_is_aggregate_;
>     typedef typename generator_of<Domain>::type proto_generator;
> 
> Or is it ?

That doesn't help. The "typename" would be incorrect (in C++03) if
Domain is not a template parameter. Sometimes I really love C++. This is
not one of those times.

I think I need to add (and test and document) a whole other collection
of macros to support this corner case. Grrrr...

Please file a bug. Thanks,

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