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// Copyright Louis Dionne 2013-2017
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
#include <boost/hana/at.hpp>
#include <boost/hana/bool.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/detail/variadic/at.hpp>
#include <boost/hana/detail/variadic/drop_into.hpp>
#include <boost/hana/detail/variadic/take.hpp>
#include <boost/hana/functional/always.hpp>
#include <boost/hana/functional/id.hpp>
#include <boost/hana/functional/on.hpp>
#include <boost/hana/fwd/append.hpp>
#include <boost/hana/fwd/at.hpp>
#include <boost/hana/fwd/concat.hpp>
#include <boost/hana/fwd/concept/sequence.hpp>
#include <boost/hana/fwd/core/make.hpp>
#include <boost/hana/fwd/drop_front.hpp>
#include <boost/hana/fwd/empty.hpp>
#include <boost/hana/fwd/front.hpp>
#include <boost/hana/fwd/prepend.hpp>
#include <boost/hana/fwd/take_front.hpp>
#include <boost/hana/fwd/transform.hpp>
#include <boost/hana/fwd/unpack.hpp>
#include <boost/hana/fwd/zip_shortest_with.hpp>
#include <boost/hana/integral_constant.hpp>
#include <boost/hana/is_empty.hpp>
#include <boost/hana/length.hpp>
#include <boost/hana/min.hpp>
#include <boost/hana/minimum.hpp>
#include <boost/hana/range.hpp>
#include <boost/hana/unpack.hpp>
#include <utility>
namespace hana = boost::hana;
// An interesting way of implementing tuple using lambda captures.
struct lambda_tuple_tag { };
template <typename Storage>
struct lambda_tuple_t {
explicit constexpr lambda_tuple_t(Storage&& s)
: storage(std::move(s))
{ }
using hana_tag = lambda_tuple_tag;
Storage storage;
};
auto lambda_tuple = [](auto ...xs) {
auto storage = [=](auto f) -> decltype(auto) { return f(xs...); };
return lambda_tuple_t<decltype(storage)>{std::move(storage)};
};
namespace boost { namespace hana {
//////////////////////////////////////////////////////////////////////////
// Foldable
//////////////////////////////////////////////////////////////////////////
template <>
struct unpack_impl<lambda_tuple_tag> {
template <typename Xs, typename F>
static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
return static_cast<Xs&&>(xs).storage(static_cast<F&&>(f));
}
};
//////////////////////////////////////////////////////////////////////////
// Functor
//////////////////////////////////////////////////////////////////////////
template <>
struct transform_impl<lambda_tuple_tag> {
template <typename Xs, typename F>
static constexpr decltype(auto) apply(Xs&& xs, F f) {
return static_cast<Xs&&>(xs).storage(
[f(std::move(f))](auto&& ...xs) -> decltype(auto) {
return lambda_tuple(f(static_cast<decltype(xs)&&>(xs))...);
}
);
}
};
//////////////////////////////////////////////////////////////////////////
// Iterable
//////////////////////////////////////////////////////////////////////////
template <>
struct front_impl<lambda_tuple_tag> {
template <typename Xs>
static constexpr decltype(auto) apply(Xs&& xs) {
return static_cast<Xs&&>(xs).storage(
[](auto&& x, auto&& ...) -> decltype(auto) {
return id(static_cast<decltype(x)&&>(x));
}
);
}
};
template <>
struct is_empty_impl<lambda_tuple_tag> {
template <typename Xs>
static constexpr decltype(auto) apply(Xs&& xs) {
return static_cast<Xs&&>(xs).storage(
[](auto const& ...xs) -> decltype(auto) {
return hana::bool_c<sizeof...(xs) == 0>;
}
);
}
};
template <>
struct at_impl<lambda_tuple_tag> {
template <typename Xs, typename Index>
static constexpr decltype(auto) apply(Xs&& xs, Index const&) {
return static_cast<Xs&&>(xs).storage(
detail::variadic::at<Index::value>
);
}
};
template <>
struct drop_front_impl<lambda_tuple_tag> {
template <typename Xs, typename N>
static constexpr decltype(auto) apply(Xs&& xs, N const& n) {
auto m = min(n, length(xs));
return static_cast<Xs&&>(xs).storage(
detail::variadic::drop_into<hana::value(m)>(lambda_tuple)
);
}
};
//////////////////////////////////////////////////////////////////////////
// MonadPlus
//////////////////////////////////////////////////////////////////////////
template <>
struct concat_impl<lambda_tuple_tag> {
template <typename Xs, typename Ys>
static constexpr decltype(auto) apply(Xs&& xs, Ys&& ys) {
return static_cast<Xs&&>(xs).storage(
[ys(static_cast<Ys&&>(ys))](auto&& ...xs) -> decltype(auto) {
return std::move(ys).storage(
// We can't initialize the capture with perfect
// forwarding since that's not supported by the
// language.
[=](auto&& ...ys) -> decltype(auto) {
return lambda_tuple(
std::move(xs)...,
static_cast<decltype(ys)&&>(ys)...
);
}
);
}
);
}
};
template <>
struct prepend_impl<lambda_tuple_tag> {
template <typename Xs, typename X>
static constexpr decltype(auto) apply(Xs&& xs, X&& x) {
return static_cast<Xs&&>(xs).storage(
[x(static_cast<X&&>(x))](auto&& ...xs) -> decltype(auto) {
return lambda_tuple(
std::move(x),
static_cast<decltype(xs)&&>(xs)...
);
}
);
}
};
template <>
struct append_impl<lambda_tuple_tag> {
template <typename Xs, typename X>
static constexpr decltype(auto) apply(Xs&& xs, X&& x) {
return static_cast<Xs&&>(xs).storage(
[x(static_cast<X&&>(x))](auto&& ...xs) -> decltype(auto) {
return lambda_tuple(
static_cast<decltype(xs)&&>(xs)...,
std::move(x)
);
}
);
}
};
template <>
struct empty_impl<lambda_tuple_tag> {
static BOOST_HANA_CONSTEXPR_LAMBDA decltype(auto) apply() {
return lambda_tuple();
}
};
//////////////////////////////////////////////////////////////////////////
// Sequence
//////////////////////////////////////////////////////////////////////////
template <>
struct Sequence<lambda_tuple_tag> {
static constexpr bool value = true;
};
template <>
struct take_front_impl<lambda_tuple_tag> {
template <typename Xs, typename N>
static constexpr decltype(auto) apply(Xs&& xs, N const& n) {
auto m = min(n, length(xs));
return static_cast<Xs&&>(xs).storage(
detail::variadic::take<decltype(m)::value>
)(lambda_tuple);
}
};
template <>
struct zip_shortest_with_impl<lambda_tuple_tag> {
template <typename F, typename ...Xss>
static constexpr auto apply(F f, Xss ...tuples) {
auto go = [=](auto index, auto ...nothing) {
return always(f)(nothing...)(at(tuples, index)...);
};
auto zip_length = minimum(lambda_tuple(length(tuples)...));
return unpack(make_range(size_c<0>, zip_length),
on(lambda_tuple, go)
);
}
};
//////////////////////////////////////////////////////////////////////////
// make
//////////////////////////////////////////////////////////////////////////
template <>
struct make_impl<lambda_tuple_tag> {
template <typename ...Xs>
static constexpr decltype(auto) apply(Xs&& ...xs) {
return lambda_tuple(static_cast<Xs&&>(xs)...);
}
};
}} // end namespace boost::hana
int main() {
auto xs = lambda_tuple(1, '2', 3.3);
static_assert(!decltype(hana::is_empty(xs))::value, "");
}
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