ceph/src/boost/boost/histogram/detail/accumulator_traits.hpp

   1 // Copyright 2019 Hans Dembinski
   2 //
   3 // Distributed under the Boost Software License, Version 1.0.
   4 // (See accompanying file LICENSE_1_0.txt
   5 // or copy at http://www.boost.org/LICENSE_1_0.txt)
   6
   7 #ifndef BOOST_HISTOGRAM_DETAIL_ACCUMULATOR_TRAITS_HPP
   8 #define BOOST_HISTOGRAM_DETAIL_ACCUMULATOR_TRAITS_HPP
   9
  10 #include <boost/histogram/detail/priority.hpp>
  11 #include <boost/histogram/fwd.hpp>
  12 #include <tuple>
  13 #include <type_traits>
  14
  15 namespace boost {
  16
  17 // forward declare accumulator_set so that it can be matched below
  18 namespace accumulators {
  19 template <class, class, class>
  20 struct accumulator_set;
  21 }
  22
  23 namespace histogram {
  24 namespace detail {
  25
  26 template <bool WeightSupport, class... Ts>
  27 struct accumulator_traits_holder {
  28   static constexpr bool weight_support = WeightSupport;
  29   using args = std::tuple<Ts...>;
  30 };
  31
  32 // member function pointer with weight_type as first argument is better match
  33 template <class R, class T, class U, class... Ts>
  34 accumulator_traits_holder<true, Ts...> accumulator_traits_impl_call_op(
  35     R (T::*)(boost::histogram::weight_type<U>, Ts...));
  36
  37 template <class R, class T, class U, class... Ts>
  38 accumulator_traits_holder<true, Ts...> accumulator_traits_impl_call_op(
  39     R (T::*)(boost::histogram::weight_type<U>&, Ts...));
  40
  41 template <class R, class T, class U, class... Ts>
  42 accumulator_traits_holder<true, Ts...> accumulator_traits_impl_call_op(
  43     R (T::*)(boost::histogram::weight_type<U>&&, Ts...));
  44
  45 template <class R, class T, class U, class... Ts>
  46 accumulator_traits_holder<true, Ts...> accumulator_traits_impl_call_op(
  47     R (T::*)(const boost::histogram::weight_type<U>&, Ts...));
  48
  49 // member function pointer only considered if all specializations above fail
  50 template <class R, class T, class... Ts>
  51 accumulator_traits_holder<false, Ts...> accumulator_traits_impl_call_op(R (T::*)(Ts...));
  52
  53 template <class T>
  54 auto accumulator_traits_impl(T&, priority<1>)
  55     -> decltype(accumulator_traits_impl_call_op(&T::operator()));
  56
  57 template <class T>
  58 auto accumulator_traits_impl(T&, priority<1>)
  59     -> decltype(std::declval<T&>() += 0, accumulator_traits_holder<true>{});
  60
  61 template <class T>
  62 auto accumulator_traits_impl(T&, priority<0>) -> accumulator_traits_holder<false>;
  63
  64 // for boost.accumulators compatibility
  65 template <class S, class F, class W>
  66 accumulator_traits_holder<false, S> accumulator_traits_impl(
  67     boost::accumulators::accumulator_set<S, F, W>&, priority<1>) {
  68   static_assert(std::is_same<W, void>::value,
  69                 "accumulator_set with weights is not directly supported, please use "
  70                 "a wrapper class that implements the Accumulator concept");
  71 }
  72
  73 template <class T>
  74 using accumulator_traits =
  75     decltype(accumulator_traits_impl(std::declval<T&>(), priority<1>{}));
  76
  77 } // namespace detail
  78 } // namespace histogram
  79 } // namespace boost
  80
  81 #endif