Daniel Krügler wrote:
>  Hi boosters,

Hi Daniel,

> 
>  I am just doing first steps in using the boost::mpl library, which is
>  really great.
>  Obviously due to my ignorance of knowing it not better, I tried the
>  following:
> 
>  #include <boost/mpl/vector.hpp>
>  #include <boost/mpl/size.hpp>
>  #include <boost/mpl/void.hpp>
>  #include <boost/tuple/tuple.hpp>
> 
>  template<
>      typename T0 = boost::mpl::void_, typename T1 = boost::mpl::void_,
>      typename T2 = boost::mpl::void_, typename T3 = boost::mpl::void_,
>      typename T4 = boost::mpl::void_, typename T5 = boost::mpl::void_,
>      typename T6 = boost::mpl::void_, typename T7 = boost::mpl::void_,
>      typename T8 = boost::mpl::void_, typename T9 = boost::mpl::void_
>      >
>  class Test
>  {
>      typedef boost::mpl::vector<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9>
>          InternalTypeContainer;
> 
>      typedef boost::tuples::tuple<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9>
>  Tuples; // Fragile code!!
>      Tuples m_Tuple;
>  };
> 
>  typedef Test<double, char, bool> MyTypes;
> 
>  As you will belief, that will not compile successfully, because
>  boost::mpl::void_ is
>  an undefined type (similar to void) and I am trying to fill my tuple
>  partially with undefined
>  types. So my problem is:
> 
>  Does there exist a boost::mpl way (?) to define my
>  boost::tuples::tuple<> inside the given
>  Test class template until the last non-mpl::void_ is filled into it?
>  (Iteration until end??)

This won't give you an exact equivalent of
'boost::tuples::tuple<T0,...,T9> ',
but for many practical purposes it's close enough:

    template< typename Types >  struct tuple_gen
        : mpl::fold_backward<
              Types
            , boost::tuples::null_type
            , boost::tuples::cons<_2,_1> 
            > 
    {
    };


    template<
        typename T0 = boost::mpl::void_, typename T1 = boost::mpl::void_,
        typename T2 = boost::mpl::void_, typename T3 = boost::mpl::void_,
        typename T4 = boost::mpl::void_, typename T5 = boost::mpl::void_,
        typename T6 = boost::mpl::void_, typename T7 = boost::mpl::void_,
        typename T8 = boost::mpl::void_, typename T9 = boost::mpl::void_
        > 
    class Test
    {
        typedef mpl::vector<T0,T1,T2,T3,T4,T5,T6,T7,T8,T9>  types_;

        typedef typename tuple_gen<
              mpl::filter_view<
                  types_
                , mpl::not_< mpl::is_void_<_1>  >
                > 
            > ::type Tuples;

        Tuples m_Tuple;
    };


> 
>  Or does their exist another tuple class, which I should try to use at
>  this place?

Joel de Guzman's Fusion library (http://tinyurl.com/yvxzm) has the one that
is about to replace the current implementation, and much more. In general,
Fusion is definitely a must use tool if you are doing anything more than a
very basic metaprogramming with tuples.

HTH,
--
Aleksey Gurtovoy
MetaCommunications Engineering
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