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From: Marco Costalba (mcostalba_at_[hidden])
Date: 2007-10-02 06:24:47
On 10/2/07, Joel de Guzman <joel_at_[hidden]> wrote:
>
> Ok, your call, since you're the one taking the challenge anyway :)
>
I have tried to remove the dependancy from mpl library and perhaps I
have found a nice way to do it.
The key idea is to use the deinitions of
tuple<A, B, C, D>
that is (perhaps) a
cons<A, cons<B, cons<C, cons<D, null_type> > > >
So instead of the following previous code:
namespace detail
{
template <typename Seq, typename derived, int n, int size>
struct do_compose
{
typedef typename Seq::head_type head;
typedef typename Seq::tail_type tail;
typedef typename do_compose<tail, derived, n - 1, size>::type ov;
typedef overload_function<ov, derived, head> type;
};
template <typename Seq, typename derived, int size>
struct do_compose<Seq, derived, 1, size>
{
typedef typename Seq::head_type head;
typedef overload_function<final_overload_function<size>, derived,
head> type;
};
template <typename Seq>
struct compose_overload_base
{
enum { n = tuples::length<Seq>::value };
typedef overload<Seq> derived;
typedef typename do_compose<Seq, derived, n, n>::type type;
};
struct get_function
{
template <typename T>
struct apply
{
typedef boost::function<T> type;
};
};
}
template <typename Seq>
struct overload : detail::compose_overload_base<Seq>::type
{
typedef typename boost::mpl::
transform<Seq, detail::get_function>::type functions_type;
functions_type functions;
};
I could write directly
namespace detail
{
template <typename Seq, typename derived, int n, int size>
struct do_compose
{
typedef typename Seq::head_type head;
typedef typename Seq::tail_type tail;
typedef do_compose<tail, derived, n - 1, size> next;
typedef typename next::type ov;
typedef typename next::cons cons_tail;
typedef overload_function<ov, derived, head> type;
typedef tuples::cons<boost::function<head>, cons_tail> cons;
};
template <typename Seq, typename derived, int size>
struct do_compose<Seq, derived, 1, size>
{
typedef typename Seq::head_type head;
typedef final_overload_function<size> final;
typedef overload_function<final, derived, head> type;
typedef tuples::cons<head, tuple<> > cons;
};
template <typename Seq>
struct compose_overload_base : do_compose<
Seq,
overload<Seq>,
tuples::length<Seq>::value,
tuples::length<Seq>::value
> {};
}
template <typename Seq>
struct overload : detail::compose_overload_base<Seq>::type
{
typedef detail::compose_overload_base<Seq> Base;
typedef typename Base::cons functions_type;
functions_type functions; // COMPILE ERROR HERE
};
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...
Thanks a lot for your patience (I'm a newbie)
Marco
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