Re: [boost] Re: io operations for stl containers?

From: Vladimir Prus (ghost_at_[hidden])
Date: 2003-02-05 03:47:23

Terje Slettebø wrote:

>>>By the way, just for fun. Adding the following output operator for
> 
> arrays,
> 
>>>to the header I gave in the previous posting:
>>
>>>-------
>>>|O|X|O|
>>>-------
>>>|X|X|O|
>>>-------
>>>|O|O|X|
>>>-------
>>>
>>>"Shall we play a game?" :)
>>
>>Sure thing :-)
> 
> 
> I guess you maybe got the "War Games" reference? :)

Don't know what this reference is, but played that game in school.

>>2. I think that we better have separate headers for stl containers, like
>>    suggested in my original email (<boost/io/vector.hpp>, etc). That's
>>    because I'd like to output maps, but would not like to include <map>
>> when I need to output a vector.
> 
> 
> Heh, just before I got this posting, I had added the following comment in
> the header:

[...]

We're in total agreement until now.

> I'll get back to your other comments, I just need to look more into
> how it might be done.

Maybe you know a better solution already, but thinking about per-conainer
format is arrive to:

We basically need the following (note that "..." are no metacharacters)

   template<class charT, template <...> class container>
   class basic_composite_io {
       int get_pword_index();
   }

   template<class charT>
   int basic_composite_io<charT, vector<...> >::get_pword_index() {
        static int i = ios_base::xalloc();
         return i;
   }

Since we can specialize on template name, we have to fake that:

   template<class charT, class T, class A>
   int basic_composite_io<charT, vector<T, A> >::get_pword_index() {
      static int i = get_vector_pword_index();
      return i;
   }

Why can't we afford to create a function for each supported container,
make it call xalloc, and return that value. Not very nice, but works.

Another alternative is to create custom 'xalloc' which takes a string,
and does not allocate new index if an index for that string is already
allocated.

   template<class charT, class T, class A>
   int basic_composite_io<charT, vector<T, A> >::get_pword_index() {
      static int i = xalloc("std::vector");
      return i;
   }

Would this be sufficient?

- Volodya