/*!
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@file
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Adapts `boost::mpl::list` for use with Hana.
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@copyright Louis Dionne 2013-2017
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_EXT_BOOST_MPL_LIST_HPP
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#define BOOST_HANA_EXT_BOOST_MPL_LIST_HPP
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#include <boost/hana/concept/foldable.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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#include <boost/hana/ext/boost/mpl/integral_c.hpp>
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#include <boost/hana/fwd/at.hpp>
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#include <boost/hana/fwd/core/to.hpp>
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#include <boost/hana/fwd/core/tag_of.hpp>
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#include <boost/hana/fwd/drop_front.hpp>
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#include <boost/hana/fwd/equal.hpp>
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#include <boost/hana/fwd/is_empty.hpp>
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#include <boost/hana/fwd/less.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/length.hpp>
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#include <boost/hana/type.hpp>
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#include <boost/hana/unpack.hpp>
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#include <boost/mpl/at.hpp>
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#include <boost/mpl/empty.hpp>
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#include <boost/mpl/equal.hpp>
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#include <boost/mpl/list.hpp>
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#include <boost/mpl/sequence_tag.hpp>
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#include <boost/mpl/size.hpp>
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#include <cstddef>
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#include <type_traits>
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#include <utility>
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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namespace boost { namespace mpl {
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//! @ingroup group-ext-mpl
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//! Adapter for Boost.MPL lists.
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//!
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//!
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//! Modeled concepts
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//! ----------------
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//! It is possible for MPL lists to model a couple of concepts.
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//! However, because they are only able to hold types, they lack
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//! the generality required to model concepts like `Functor`,
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//! `Sequence` and other related concepts.
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//!
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//! 1. `Comparable`\n
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//! Two MPL lists are equal if and only if they contain the same
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//! number of types, and if all those types are equal.
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//! @include example/ext/boost/mpl/list/comparable.cpp
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//!
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//! 2. `Foldable`\n
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//! Folding a MPL list is equivalent to folding it as a `Sequence`.
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//! @include example/ext/boost/mpl/list/foldable.cpp
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//!
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//! 3. `Iterable`\n
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//! Iterating over a MPL list is just iterating over each of the
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//! types it contains, as if it were a `Sequence`.
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//! @include example/ext/boost/mpl/list/iterable.cpp
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//!
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//! 4. `Searchable`\n
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//! A MPL list can be searched as if it were a tuple containing
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//! `hana::type`s.
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//! @include example/ext/boost/mpl/list/searchable.cpp
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//!
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//!
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//! Conversion from any `Foldable`
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//! ------------------------------
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//! A MPL list can be created from any `Foldable`. More precisely,
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//! for a `Foldable` `xs` whose linearization is `[x1, ..., xn]`,
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//! @code
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//! to<ext::boost::mpl::list_tag>(xs) == mpl::list<t1, ..., tn>{}
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//! @endcode
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//! where `tk` is the type of `xk`, or the type contained in `xk` if
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//! `xk` is a `hana::type`.
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//! @warning
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//! The limitations on the size of `mpl::list`s are inherited by
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//! this conversion utility, and hence trying to convert a `Foldable`
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//! containing more than [BOOST_MPL_LIMIT_LIST_SIZE][1] elements is
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//! an error.
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//! @include example/ext/boost/mpl/list/conversion.cpp
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//!
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//! [1]: http://www.boost.org/doc/libs/release/libs/mpl/doc/refmanual/limit-list-size.html
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template <typename ...T>
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struct list { };
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}}
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#endif
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BOOST_HANA_NAMESPACE_BEGIN
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namespace ext { namespace boost { namespace mpl {
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using list_tag = ::boost::mpl::sequence_tag< ::boost::mpl::list<>>::type;
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}}}
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template <typename T>
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struct tag_of<T, when<
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std::is_same<
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typename ::boost::mpl::sequence_tag<T>::type,
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::boost::mpl::sequence_tag< ::boost::mpl::list<>>::type
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>::value
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>> {
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using type = ext::boost::mpl::list_tag;
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};
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//////////////////////////////////////////////////////////////////////////
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// Comparable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct equal_impl<ext::boost::mpl::list_tag, ext::boost::mpl::list_tag> {
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template <typename Xs, typename Ys>
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static constexpr auto apply(Xs const&, Ys const&) {
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return typename ::boost::mpl::equal<Xs, Ys>::type{};
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Foldable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct length_impl<ext::boost::mpl::list_tag> {
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template <typename Xs>
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static constexpr auto apply(Xs const&) {
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return hana::size_c< ::boost::mpl::size<Xs>::type::value>;
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Iterable
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct at_impl<ext::boost::mpl::list_tag> {
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template <typename Ts, typename N>
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static constexpr auto apply(Ts const&, N const&) {
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constexpr std::size_t n = N::value;
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using T = typename ::boost::mpl::at_c<Ts, n>::type;
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return hana::type_c<T>;
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}
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};
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template <>
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struct drop_front_impl<ext::boost::mpl::list_tag> {
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template <std::size_t n, typename Xs, std::size_t ...i>
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static constexpr auto drop_front_helper(Xs const&, std::index_sequence<i...>) {
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return boost::mpl::list<
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typename boost::mpl::at_c<Xs, n + i>::type...
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>{};
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}
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template <typename Xs, typename N>
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static constexpr auto apply(Xs const& xs, N const&) {
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constexpr std::size_t n = N::value;
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constexpr std::size_t len = decltype(hana::length(xs))::value;
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return drop_front_helper<n>(xs,
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std::make_index_sequence<(n < len ? len - n : 0)>{});
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}
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};
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template <>
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struct is_empty_impl<ext::boost::mpl::list_tag> {
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template <typename Xs>
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static constexpr auto apply(Xs const&)
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{ return typename ::boost::mpl::empty<Xs>::type{}; }
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};
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//////////////////////////////////////////////////////////////////////////
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// Conversion from a Foldable
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//////////////////////////////////////////////////////////////////////////
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template <typename F>
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struct to_impl<ext::boost::mpl::list_tag, F, when<hana::Foldable<F>::value>> {
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template <typename Xs>
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static constexpr decltype(auto) apply(Xs&& xs) {
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auto list_type = hana::unpack(static_cast<Xs&&>(xs),
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hana::template_<::boost::mpl::list>);
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return typename decltype(list_type)::type{};
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_EXT_BOOST_MPL_LIST_HPP
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