Re: [Boost-users] [typeof] Determining if a type has been registered or not at compile time

Subject: Re: [Boost-users] [typeof] Determining if a type has been registered or not at compile time
From: joel falcou (joel.falcou_at_[hidden])
Date: 2009-12-22 13:03:48

Edward Diener wrote:
> Is there any way one can determine whether a type has been registered 
> or not with Boost.Typeof at compile time so that the information can 
> be used in TMP ? I am thinking, of course, of the use of typeof in a 
> template, where a template parameter may or may not be aregistered 
> type when the template has been instantiated. I would like to provide 
> my own TMP fallback code if the type has not been registered rather 
> than  see an immediate compiler error generated. Something like:
>
> boost::mpl::eval_if
>   <
>   boost::typeof::registered<T>, // this would be nice to have
>   boost::mpl::identity<BOOST_TYPEOF_TPL(some_expression)>,
>   boost::mpl::identity</* use another facility to get the type I want 
> into a metafunction*/>
>   >
A simple way could be to add a meta-function specialisation in the 
typeof registration macro so that a is_registered<T> is available in a 
pervasive way.

-- 
___________________________________________
Joel Falcou - Assistant Professor
PARALL Team - LRI - Universite Paris Sud XI
Tel : [phone]