Re: [boost] Re: boost::tuple to MPL sequence

From: Aleksey Gurtovoy (agurtovoy_at_[hidden])
Date: 2003-04-29 07:33:15

Alexander Nasonov wrote:
> Alternatively, you can implement MPL conformant sequence
> tuple_sequence<Tuple>. It's not so hard as you can imagine.

It's not indeed:

template< typename Tuple > struct tuple_iterator
{
    typedef mpl::forward_iterator_tag category;
    typedef typename Tuple::head_type type;
    typedef tuple_iterator<typename Tuple::tail_type> next;
};

// end iterator
template<> struct tuple_iterator<boost::tuples::null_type>
{
    typedef mpl::forward_iterator_tag category;
};

template< typename Tuple > struct tuple_sequence
    : mpl::iterator_range<
          tuple_iterator<Tuple>
        , tuple_iterator<boost::tuples::null_type>
        >
{
};

// test
typedef boost::tuples::tuple<int,char const*,bool> t;

BOOST_STATIC_ASSERT( mpl::size< tuple_sequence<t> >::type::value == 3 );
BOOST_STATIC_ASSERT(( mpl::equal<
      tuple_sequence<t>
    , mpl::list<int,char const*,bool>
    >::type::value ));

> (Question to MPL's authors: when it will be documented?).

How to write your own iterator is partially documented here -
http://www.boost.org/libs/mpl/doc/paper/mpl_paper.html#sequences.concepts.
And then there is a reference doc -
http://www.boost.org/libs/mpl/doc/ref/Iterators.html.

And of course, anyone is always welcome to contribute more tutorials - it's
for sure will be appreciated.

Aleksey