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/*!
@file
Adapts `boost::mpl::list` for use with Hana.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_EXT_BOOST_MPL_LIST_HPP
#define BOOST_HANA_EXT_BOOST_MPL_LIST_HPP
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
#include <boost/hana/ext/boost/mpl/integral_c.hpp>
#include <boost/hana/fwd/at.hpp>
#include <boost/hana/fwd/core/to.hpp>
#include <boost/hana/fwd/core/tag_of.hpp>
#include <boost/hana/fwd/drop_front.hpp>
#include <boost/hana/fwd/equal.hpp>
#include <boost/hana/fwd/is_empty.hpp>
#include <boost/hana/fwd/less.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/length.hpp>
#include <boost/hana/type.hpp>
#include <boost/hana/unpack.hpp>
#include <boost/mpl/at.hpp>
#include <boost/mpl/empty.hpp>
#include <boost/mpl/equal.hpp>
#include <boost/mpl/list.hpp>
#include <boost/mpl/sequence_tag.hpp>
#include <boost/mpl/size.hpp>
#include <cstddef>
#include <type_traits>
#include <utility>
#ifdef BOOST_HANA_DOXYGEN_INVOKED
namespace boost { namespace mpl {
//! @ingroup group-ext-mpl
//! Adapter for Boost.MPL lists.
//!
//!
//! Modeled concepts
//! ----------------
//! It is possible for MPL lists to model a couple of concepts.
//! However, because they are only able to hold types, they lack
//! the generality required to model concepts like `Functor`,
//! `Sequence` and other related concepts.
//!
//! 1. `Comparable`\n
//! Two MPL lists are equal if and only if they contain the same
//! number of types, and if all those types are equal.
//! @include example/ext/boost/mpl/list/comparable.cpp
//!
//! 2. `Foldable`\n
//! Folding a MPL list is equivalent to folding it as a `Sequence`.
//! @include example/ext/boost/mpl/list/foldable.cpp
//!
//! 3. `Iterable`\n
//! Iterating over a MPL list is just iterating over each of the
//! types it contains, as if it were a `Sequence`.
//! @include example/ext/boost/mpl/list/iterable.cpp
//!
//! 4. `Searchable`\n
//! A MPL list can be searched as if it were a tuple containing
//! `hana::type`s.
//! @include example/ext/boost/mpl/list/searchable.cpp
//!
//!
//! Conversion from any `Foldable`
//! ------------------------------
//! A MPL list can be created from any `Foldable`. More precisely,
//! for a `Foldable` `xs` whose linearization is `[x1, ..., xn]`,
//! @code
//! to<ext::boost::mpl::list_tag>(xs) == mpl::list<t1, ..., tn>{}
//! @endcode
//! where `tk` is the type of `xk`, or the type contained in `xk` if
//! `xk` is a `hana::type`.
//! @warning
//! The limitations on the size of `mpl::list`s are inherited by
//! this conversion utility, and hence trying to convert a `Foldable`
//! containing more than [BOOST_MPL_LIMIT_LIST_SIZE][1] elements is
//! an error.
//! @include example/ext/boost/mpl/list/conversion.cpp
//!
//! [1]: http://www.boost.org/doc/libs/release/libs/mpl/doc/refmanual/limit-list-size.html
template <typename ...T>
struct list { };
}}
#endif
namespace boost { namespace hana {
namespace ext { namespace boost { namespace mpl {
using list_tag = ::boost::mpl::sequence_tag< ::boost::mpl::list<>>::type;
}}}
template <typename T>
struct tag_of<T, when<
std::is_same<
typename ::boost::mpl::sequence_tag<T>::type,
::boost::mpl::sequence_tag< ::boost::mpl::list<>>::type
>::value
>> {
using type = ext::boost::mpl::list_tag;
};
//////////////////////////////////////////////////////////////////////////
// Comparable
//////////////////////////////////////////////////////////////////////////
template <>
struct equal_impl<ext::boost::mpl::list_tag, ext::boost::mpl::list_tag> {
template <typename Xs, typename Ys>
static constexpr auto apply(Xs const&, Ys const&) {
return typename ::boost::mpl::equal<Xs, Ys>::type{};
}
};
//////////////////////////////////////////////////////////////////////////
// Foldable
//////////////////////////////////////////////////////////////////////////
template <>
struct length_impl<ext::boost::mpl::list_tag> {
template <typename Xs>
static constexpr auto apply(Xs const&) {
return hana::size_c< ::boost::mpl::size<Xs>::type::value>;
}
};
//////////////////////////////////////////////////////////////////////////
// Iterable
//////////////////////////////////////////////////////////////////////////
template <>
struct at_impl<ext::boost::mpl::list_tag> {
template <typename Ts, typename N>
static constexpr auto apply(Ts const&, N const&) {
constexpr std::size_t n = N::value;
using T = typename ::boost::mpl::at_c<Ts, n>::type;
return hana::type_c<T>;
}
};
template <>
struct drop_front_impl<ext::boost::mpl::list_tag> {
template <std::size_t n, typename Xs, std::size_t ...i>
static constexpr auto drop_front_helper(Xs const&, std::index_sequence<i...>) {
return boost::mpl::list<
typename boost::mpl::at_c<Xs, n + i>::type...
>{};
}
template <typename Xs, typename N>
static constexpr auto apply(Xs const& xs, N const&) {
constexpr std::size_t n = N::value;
constexpr std::size_t len = decltype(hana::length(xs))::value;
return drop_front_helper<n>(xs,
std::make_index_sequence<(n < len ? len - n : 0)>{});
}
};
template <>
struct is_empty_impl<ext::boost::mpl::list_tag> {
template <typename Xs>
static constexpr auto apply(Xs const&)
{ return typename ::boost::mpl::empty<Xs>::type{}; }
};
//////////////////////////////////////////////////////////////////////////
// Conversion from a Foldable
//////////////////////////////////////////////////////////////////////////
template <typename F>
struct to_impl<ext::boost::mpl::list_tag, F, when<hana::Foldable<F>::value>> {
template <typename Xs>
static constexpr decltype(auto) apply(Xs&& xs) {
auto list_type = hana::unpack(static_cast<Xs&&>(xs),
hana::template_<::boost::mpl::list>);
return typename decltype(list_type)::type{};
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_EXT_BOOST_MPL_LIST_HPP
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