projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Defines `boost::hana::zero`. | |
| 4 | ||
| 5 | @copyright Louis Dionne 2013-2016 | |
| 6 | Distributed under the Boost Software License, Version 1.0. | |
| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
| 8 | */ | |
| 9 | ||
| 10 | #ifndef BOOST_HANA_ZERO_HPP | |
| 11 | #define BOOST_HANA_ZERO_HPP | |
| 12 | ||
| 13 | #include <boost/hana/fwd/zero.hpp> | |
| 14 | ||
| 15 | #include <boost/hana/concept/constant.hpp> | |
| 16 | #include <boost/hana/concept/monoid.hpp> | |
| 17 | #include <boost/hana/config.hpp> | |
| 18 | #include <boost/hana/core/to.hpp> | |
| 19 | #include <boost/hana/core/dispatch.hpp> | |
| 20 | #include <boost/hana/detail/canonical_constant.hpp> | |
| 21 | ||
| 22 | #include <type_traits> | |
| 23 | ||
| 24 | ||
| 25 | BOOST_HANA_NAMESPACE_BEGIN | |
| 26 | template <typename M> | |
| 27 | struct zero_t { | |
| 28 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
| 29 | static_assert(hana::Monoid<M>::value, | |
| 30 | "hana::zero<M>() requires 'M' to be a Monoid"); | |
| 31 | #endif | |
| 32 | ||
| 33 | constexpr decltype(auto) operator()() const { | |
| 34 | using Zero = BOOST_HANA_DISPATCH_IF(zero_impl<M>, | |
| 35 | hana::Monoid<M>::value | |
| 36 | ); | |
| 37 | ||
| 38 | return Zero::apply(); | |
| 39 | } | |
| 40 | }; | |
| 41 | ||
| 42 | template <typename M, bool condition> | |
| 43 | struct zero_impl<M, when<condition>> : default_ { | |
| 44 | template <typename ...Args> | |
| 45 | static constexpr auto apply(Args&& ...) = delete; | |
| 46 | }; | |
| 47 | ||
| 48 | ////////////////////////////////////////////////////////////////////////// | |
| 49 | // Model for non-boolean arithmetic data types | |
| 50 | ////////////////////////////////////////////////////////////////////////// | |
| 51 | template <typename T> | |
| 52 | struct zero_impl<T, when< | |
| 53 | std::is_arithmetic<T>::value && | |
| 54 | !std::is_same<T, bool>::value | |
| 55 | >> { | |
| 56 | static constexpr T apply() | |
| 57 | { return static_cast<T>(0); } | |
| 58 | }; | |
| 59 | ||
| 60 | ////////////////////////////////////////////////////////////////////////// | |
| 61 | // Model for Constants over a Monoid | |
| 62 | ////////////////////////////////////////////////////////////////////////// | |
| 63 | namespace detail { | |
| 64 | template <typename C> | |
| 65 | struct constant_from_zero { | |
| 66 | static constexpr auto value = hana::zero<typename C::value_type>(); | |
| 67 | using hana_tag = detail::CanonicalConstant<typename C::value_type>; | |
| 68 | }; | |
| 69 | } | |
| 70 | ||
| 71 | template <typename C> | |
| 72 | struct zero_impl<C, when< | |
| 73 | hana::Constant<C>::value && | |
| 74 | Monoid<typename C::value_type>::value | |
| 75 | >> { | |
| 76 | static constexpr decltype(auto) apply() | |
| 77 | { return hana::to<C>(detail::constant_from_zero<C>{}); } | |
| 78 | }; | |
| 79 | BOOST_HANA_NAMESPACE_END | |
| 80 | ||
| 81 | #endif // !BOOST_HANA_ZERO_HPP |