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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/assert.hpp>
- #include <boost/hana/chain.hpp>
- #include <boost/hana/equal.hpp>
- #include <boost/hana/for_each.hpp>
- #include <boost/hana/traits.hpp>
- #include <boost/hana/tuple.hpp>
- #include <boost/hana/type.hpp>
- #include <type_traits>
- #include <utility>
- namespace hana = boost::hana;
- // Using the `tuple` Monad, we generate all the possible combinations of
- // cv-qualifiers and reference qualifiers. Then, we use the `optional`
- // Monad to make sure that our generic function can be called with
- // arguments of any of those types.
- // cv_qualifiers : type -> tuple(type)
- auto cv_qualifiers = [](auto t) {
- return hana::make_tuple(
- t,
- hana::traits::add_const(t),
- hana::traits::add_volatile(t),
- hana::traits::add_volatile(hana::traits::add_const(t))
- );
- };
- // ref_qualifiers : type -> tuple(type)
- auto ref_qualifiers = [](auto t) {
- return hana::make_tuple(
- hana::traits::add_lvalue_reference(t),
- hana::traits::add_rvalue_reference(t)
- );
- };
- auto possible_args = cv_qualifiers(hana::type_c<int>) | ref_qualifiers;
- BOOST_HANA_CONSTANT_CHECK(
- possible_args == hana::make_tuple(
- hana::type_c<int&>,
- hana::type_c<int&&>,
- hana::type_c<int const&>,
- hana::type_c<int const&&>,
- hana::type_c<int volatile&>,
- hana::type_c<int volatile&&>,
- hana::type_c<int const volatile&>,
- hana::type_c<int const volatile&&>
- )
- );
- struct some_function {
- template <typename T>
- void operator()(T&&) const { }
- };
- int main() {
- hana::for_each(possible_args, [](auto t) {
- using T = typename decltype(t)::type;
- static_assert(decltype(hana::is_valid(some_function{})(std::declval<T>())){},
- "some_function should be callable with any type of argument");
- });
- }
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