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1// Copyright John Maddock 2007.2// Copyright Matt Borland 2021.3// Use, modification and distribution are subject to the4// Boost Software License, Version 1.0. (See accompanying file5// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)6 7/*8This header defines two traits classes, both in namespace boost::math::tools.9 10is_distribution<D>::value is true iff D has overloaded "cdf" and11"quantile" functions, plus member typedefs value_type and policy_type. 12It's not much of a definitive test frankly,13but if it looks like a distribution and quacks like a distribution14then it must be a distribution.15 16is_scaled_distribution<D>::value is true iff D is a distribution17as defined above, and has member functions "scale" and "location".18 19*/20 21#ifndef BOOST_STATS_IS_DISTRIBUTION_HPP22#define BOOST_STATS_IS_DISTRIBUTION_HPP23 24#ifdef _MSC_VER25#pragma once26#endif27 28#include <type_traits>29 30namespace boost{ namespace math{ namespace tools{31 32namespace detail{33 34#define BOOST_MATH_HAS_NAMED_TRAIT(trait, name) \35template <typename T> \36class trait \37{ \38private: \39 using yes = char; \40 struct no { char x[2]; }; \41 \42 template <typename U> \43 static yes test(typename U::name* = nullptr); \44 \45 template <typename U> \46 static no test(...); \47 \48public: \49 static constexpr bool value = (sizeof(test<T>(0)) == sizeof(char)); \50};51 52BOOST_MATH_HAS_NAMED_TRAIT(has_value_type, value_type)53BOOST_MATH_HAS_NAMED_TRAIT(has_policy_type, policy_type)54BOOST_MATH_HAS_NAMED_TRAIT(has_backend_type, backend_type)55 56// C++17-esque helpers57#if defined(__cpp_variable_templates) && __cpp_variable_templates >= 201304L58template <typename T>59constexpr bool has_value_type_v = has_value_type<T>::value;60 61template <typename T>62constexpr bool has_policy_type_v = has_policy_type<T>::value;63 64template <typename T>65constexpr bool has_backend_type_v = has_backend_type<T>::value;66#endif67 68template <typename D>69char cdf(const D&, ...);70template <typename D>71char quantile(const D&, ...);72 73template <typename D>74struct has_cdf75{76 static D d;77 static constexpr bool value = sizeof(cdf(d, 0.0f)) != 1;78};79 80template <typename D>81struct has_quantile82{83 static D d;84 static constexpr bool value = sizeof(quantile(d, 0.0f)) != 1;85};86 87template <typename D>88struct is_distribution_imp89{90 static constexpr bool value =91 has_quantile<D>::value 92 && has_cdf<D>::value93 && has_value_type<D>::value94 && has_policy_type<D>::value;95};96 97template <typename sig, sig val>98struct result_tag{};99 100template <typename D>101double test_has_location(const volatile result_tag<typename D::value_type (D::*)()const, &D::location>*);102template <typename D>103char test_has_location(...);104 105template <typename D>106double test_has_scale(const volatile result_tag<typename D::value_type (D::*)()const, &D::scale>*);107template <typename D>108char test_has_scale(...);109 110template <typename D, bool b>111struct is_scaled_distribution_helper112{113 static constexpr bool value = false;114};115 116template <typename D>117struct is_scaled_distribution_helper<D, true>118{119 static constexpr bool value = 120 (sizeof(test_has_location<D>(0)) != 1) 121 && 122 (sizeof(test_has_scale<D>(0)) != 1);123};124 125template <typename D>126struct is_scaled_distribution_imp127{128 static constexpr bool value = (::boost::math::tools::detail::is_scaled_distribution_helper<D, ::boost::math::tools::detail::is_distribution_imp<D>::value>::value);129};130 131} // namespace detail132 133template <typename T> struct is_distribution : public std::integral_constant<bool, ::boost::math::tools::detail::is_distribution_imp<T>::value> {};134template <typename T> struct is_scaled_distribution : public std::integral_constant<bool, ::boost::math::tools::detail::is_scaled_distribution_imp<T>::value> {};135 136}}}137 138#endif139 140 141