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From: Marco (mrcekets_at_[hidden])
Date: 2007-10-02 13:46:17
On Tue, 02 Oct 2007 12:24:47 +0200, Marco Costalba <mcostalba_at_[hidden]>
wrote:
skip
>
> I could write directly
>
>
skip
>
> typedef overload_function<final, derived, head> type;
> typedef tuples::cons<head, tuple<> > cons;
> };
>
>
Maybe you should replace tuple<> with tuples::null_type ...
skip
> But I have an error as soon as I try to instantiate 'functions_type'
>
> The compile error seems very internal to tuple library and an help on
> how to come up with this would be very apreciated...
>
... but I don't know if this is the only problem.
However your last changes makes the code too complicated, IMO.
I made up a metafunction called wrapper that should do the work.
examples:
(1)
typedef tuple<int, double, char> fund_types;
typedef wrapper<fund_types, vector>::type vectors;
BOOST_STATIC_ASSERT((
is_same< vectors,
cons<vector<int>,
cons<vector<double>,
cons<vector<char>,
null_type
>
>
>
> ));
(2)
typedef tuple<
int(char)
, double(int, char)
, char(std::string)
>
signatures;
typedef wrapper<signatures, boost::function>::type functions;
BOOST_STATIC_ASSERT((
is_same< functions,
cons<function<int(char)>,
cons<function<double(int, char)>,
cons<function<char(std::string)>,
null_type
>
>
>
> ));
Here follow the code for the metafunction:
namespace boost { namespace detail {
template<
typename Seq,
template<typename > class TT,
unsigned int N = tuples::length<Seq>::value
>
struct wrapper
{
typedef typename Seq::head_type head;
typedef typename Seq::tail_type tail;
typedef TT<head> new_head;
typedef typename wrapper<tail, TT>::type new_tail;
typedef
tuples::cons< new_head, new_tail >
type;
};
template< typename Seq, template<typename > class TT>
struct wrapper<Seq, TT, 0>
{
typedef tuples::null_type type;
};
} } // end namespaces
I used it inside the overload struct replacing the code:
typedef typename tuples::element<0, Seq>::type Sig0;
typedef typename tuples::element<1, Seq>::type Sig1;
typedef typename tuples::element<2, Seq>::type Sig2;
typedef typename tuples::element<3, Seq>::type Sig3;
typedef
tuple<
boost::function<Sig0>
, boost::function<Sig1>
, boost::function<Sig2>
, boost::function<Sig3>
>
functions_type;
with a single line :
typedef
typename detail::wrapper<Seq, boost::function>::type
functions_type;
... and all seems to work correctly. I tested it with gcc 4.1.2 and boost
1.33.1 under linux.
Moreover the wrapper metafunction can be used in other context too.
The question is :
it's ok to use cons< cons < ... >, ..., null_type > instead of tuple type ?
Regards,
Marco Cecchetti
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