ceph/src/boost/libs/hana/include/boost/hana/core/common.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::common` and `boost::hana::common_t`.
   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_CORE_COMMON_HPP
  11 #define BOOST_HANA_CORE_COMMON_HPP
  12
  13 #include <boost/hana/fwd/core/common.hpp>
  14
  15 #include <boost/hana/concept/constant.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/when.hpp>
  18 #include <boost/hana/detail/canonical_constant.hpp>
  19 #include <boost/hana/detail/std_common_type.hpp>
  20 #include <boost/hana/detail/void_t.hpp>
  21
  22 #include <type_traits>
  23
  24
  25 BOOST_HANA_NAMESPACE_BEGIN
  26     //////////////////////////////////////////////////////////////////////////
  27     // common
  28     //////////////////////////////////////////////////////////////////////////
  29     //! @cond
  30     template <typename T, typename U, typename>
  31     struct common : common<T, U, when<true>> { };
  32     //! @endcond
  33
  34     template <typename T, typename U, bool condition>
  35     struct common<T, U, when<condition>>
  36         : detail::std_common_type<T, U>
  37     { };
  38
  39     template <typename T>
  40     struct common<T, T> {
  41         using type = T;
  42     };
  43
  44     //////////////////////////////////////////////////////////////////////////
  45     // has_common
  46     //////////////////////////////////////////////////////////////////////////
  47     template <typename T, typename U, typename>
  48     struct has_common : std::false_type { };
  49
  50     template <typename T, typename U>
  51     struct has_common<T, U, detail::void_t<typename common<T, U>::type>>
  52         : std::true_type
  53     { };
  54
  55     //////////////////////////////////////////////////////////////////////////
  56     // Provided common data types for Constants
  57     //////////////////////////////////////////////////////////////////////////
  58     namespace constant_detail {
  59         //! @todo
  60         //! This is an awful hack to avoid having
  61         //! @code
  62         //!     common<integral_constant_tag<int>, integral_constant_tag<long>>
  63         //!         ==
  64         //!     CanonicalConstant<long>
  65         //! @endcode
  66         template <typename A, typename B, typename C>
  67         struct which {
  68             using type = detail::CanonicalConstant<C>;
  69         };
  70
  71         template <template <typename ...> class A, typename T, typename U, typename C>
  72         struct which<A<T>, A<U>, C> {
  73             using type = A<C>;
  74         };
  75     }
  76
  77     template <typename A, typename B>
  78     struct common<A, B, when<
  79         hana::Constant<A>::value &&
  80         hana::Constant<B>::value &&
  81         has_common<typename A::value_type, typename B::value_type>::value
  82     >> {
  83         using type = typename constant_detail::which<
  84             A, B,
  85             typename common<typename A::value_type,
  86                             typename B::value_type>::type
  87         >::type;
  88     };
  89
  90     template <typename A, typename B>
  91     struct common<A, B, when<
  92         hana::Constant<A>::value &&
  93         !hana::Constant<B>::value &&
  94         has_common<typename A::value_type, B>::value
  95     >> {
  96         using type = typename common<typename A::value_type, B>::type;
  97     };
  98
  99     template <typename A, typename B>
 100     struct common<A, B, when<
 101         !hana::Constant<A>::value &&
 102         hana::Constant<B>::value &&
 103         has_common<A, typename B::value_type>::value
 104     >> {
 105         using type = typename common<A, typename B::value_type>::type;
 106     };
 107 BOOST_HANA_NAMESPACE_END
 108
 109 #endif // !BOOST_HANA_CORE_COMMON_HPP