Re: [boost] [review][mp11] Reminder of ongoing formal review

Subject: Re: [boost] [review][mp11] Reminder of ongoing formal review
From: Roberto Hinz (robhz786_at_[hidden])
Date: 2017-07-23 02:39:20

Hi,

not a review yet.
I´m just wondering: would the implementation below perfom better than the
recursive version of mp_find_impl ?
I think it should perform better when one uses mp_find several times in the
same list.
It also compiles in vs2013.

template <class ... T> struct mp_find_impl_helper;

template <> struct mp_find_impl_helper<>
{
    struct tag {};
    static mp_size_t<0> get(const tag&, ...);
};

template <class T, class ... Rest>
struct mp_find_impl_helper<T, Rest...> : mp_find_impl_helper<Rest...>
{
    using mp_find_impl_helper<Rest...>::get;

    using parent_tag = typename mp_find_impl_helper<Rest...>::tag;

    struct tag : parent_tag {};

    static mp_size_t<1 + sizeof...(Rest)> get(const tag&, mp_identity<T>);
};

template<class L, class V> struct mp_find_impl;

template <template <class ...> class L, class ... T, class V>
struct mp_find_impl<L<T...>, V>
{
    using helper = mp_find_impl_helper<T...>;

    using tag = typename helper::tag;

    using R = decltype(helper::get(tag(), mp_identity<V>()));

    using type = mp_size_t<sizeof...(T) - R::value>;
};

// Regargs
// robhz