[boost] Re: Partially specializing less<> with nested template class

From: Larry Evans (cppljevans_at_[hidden])
Date: 2004-07-08 16:51:41

On 07/08/2004 04:34 PM, David B. Held wrote:
> Jonathan Turkanis wrote:
> 
>> [...]
>> Could you pull the definition of nested outside of sp
>>
>>     template<typename P1, typename P2, typename T>
>>     struct sp_nested { };
>>
>> then use a metafunction within sp:
>>
>>     template<typename P1, typename P2>
>>     struct sp {
>>          template<typename T>
>>          struct nested {
>>              typedef sp_nested<P1, P2, T> type;
>>          };
>>     };
>> [...]
> 
> 
> For syntax reasons, this is an undesirable solution.  Although,
> you could get pretty close by modifying it a little:
> 
>      template<typename P1, typename P2>
>      struct sp {
>           template<typename T>
>           struct nested : sp_nested<P1, P2, T>
>           { };
>      };
> 
>> [...]
>> You can then make less< sp_nested<P1, P2, T> > do pretty much
> 
>  > whatever you want; the question is whether you can make the
>  > metafunction do whatever you needed the nested template to do.
> 
> The problem is that sp_nested<> would be an implementation detail
> that I would not want to expose to the user.  So I would not want
> the user to have to mention it in order to instantiate less<>.

FWIW, there's rm_nondeduced at:

http://cvs.sourceforge.net/viewcvs.py/boost-sandbox/boost-sandbox/boost/managed_ptr/rm_nondeduced.hpp

which is vaguely similar to some of previous ideas. It's used at:

   cycle_basis_mgr.hpp
   refcycle_prox_visitor_abs.hpp

It's just another variation and hopefully you can maybe merge the
ideas and distill the best from all of them.