Re: [boost] [parameter] function types as named template parameters?

Subject: Re: [boost] [parameter] function types as named template parameters?
From: David Abrahams (dave_at_[hidden])
Date: 2009-01-23 00:55:36

on Thu Jan 22 2009, Frank Mori Hess <frank.hess-AT-nist.gov> wrote:

> Does Boost.Parameter support function types as named template type parameters?  
> I'm trying to write a metafunction which lets you use Boost.Parameter to 
> specify the template types for a boost::signals2::signal using named type 
> parameters, as was suggested during the review.  But it doesn't seem to work 
> for the "Signature" function type.  I get errors like:
>
> /home/fhess/svn/boost/boost/parameter/aux_/arg_list.hpp:264: error: function 
> returning a function
> /home/fhess/svn/boost/boost/parameter/aux_/arg_list.hpp:270: error: function 
> returning a function
> /home/fhess/svn/boost/boost/parameter/aux_/arg_list.hpp:352: error: function 
> returning a function
> /home/fhess/svn/boost/boost/parameter/aux_/arg_list.hpp:359: error: function 
> returning a function
> /home/fhess/svn/boost/boost/parameter/aux_/arg_list.hpp:365: error: function 
> returning a function

It wouldn't surprise me if we had overlooked that possibility.

> I can get it to work if I don't use Boost.Parameter for the "Signature" type, 
> but only use it for the other 6 types.

Can you post a minimal example that reproduces this bug?  I'm sure
there's a quick fix.

> Also, I noticed BOOST_PARAMETER_MAX_ARITY defaults to 5, but signals2::signal 
> has 7 parameters.  I can't reliably redefine BOOST_PARAMETER_MAX_ARITY in my 
> library header, since it must be defined before boost/parameter/config.hpp 
> gets included.  You can't redefine the arity and then re-include the 
> parameter library headers like you can with Boost.Function.

Oh, that's cool.  Please open a ticket with a feature request for that
and assign it to Daniel Wallin.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com