Re: [Boost-users] Tuple use/overuse?

From: Roman Perepelitsa (roman.perepelitsa_at_[hidden])
Date: 2007-07-26 03:18:43

> Joel de Guzman <joel_at_[hidden]> on Thu, 26 Jul 2007 06:59:46 
+0800
> > - bind expression with tuple becomes a nightmare
> 
> Why? Ah access to the members?

It's a nightmare indeed. I'd say boost::get is not bindable at all.

typedef tuple<int, double> two;
vector<two> src;
vector<int> dst;

// ouch
const int & (*get_first)(const cons<two::head_type,
                            two::tail_type> &) = get<0>;

transform(src.begin(), src.end(), dst.begin(), get_first);

Would not it be cool to write something like this instead?

transform(src.begin(), src.end(), dst.begin(), get<0>());

And it's not hard to implement it.

namespace boost {
namespace tuples
{
    template <int N>
    struct getter
    {
        template <class HT, class TT>
        typename access_traits<
            typename element<N, cons<HT, TT> >::type
        >::non_const_type
        operator()(cons<HT, TT> & c) const
        {
            return get<N>(c);
        }

        template <class HT, class TT>
        typename access_traits<
            typename element<N, cons<HT, TT> >::type
        >::const_type
        operator()(const cons<HT, TT> & c) const
        {
            return get<N>(c);
        }
    };
}

template <int N>
tuples::getter<N> get()
{
    return tuples::getter<N>();
}
}

Does fusion have something like this?

Regards,
Roman Perepelitsa

Deutsche Bank Moscow
[phone]

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