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Add BEAST_DEFINE_IS_CALL_POSSIBLE metaprogramming macro
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Vinnie Falco
@@ -17,8 +17,252 @@
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*/
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//==============================================================================
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#ifndef BEAST_FUNCTIONAL_BEASTHEADER
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#define BEAST_FUNCTIONAL_BEASTHEADER
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#ifndef BEAST_FUNCTIONAL_H_INCLUDED
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#define BEAST_FUNCTIONAL_H_INCLUDED
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//------------------------------------------------------------------------------
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// inspired by Roman Perepelitsa's presentation from comp.lang.c++.moderated
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// based on the implementation here: http://www.rsdn.ru/forum/cpp/2759773.1.aspx
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//
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namespace is_call_possible_detail
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{
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template<typename T>
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struct add_reference
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{
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typedef T& type;
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};
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template<typename T>
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struct add_reference<T&>
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{
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typedef T& type;
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};
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template <typename T> class void_exp_result {};
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template <typename T, typename U>
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U const& operator,(U const&, void_exp_result<T>);
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template <typename T, typename U>
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U& operator,(U&, void_exp_result<T>);
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template <typename src_type, typename dest_type>
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struct clone_constness
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{
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typedef dest_type type;
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};
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template <typename src_type, typename dest_type>
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struct clone_constness<const src_type, dest_type>
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{
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typedef const dest_type type;
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};
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}
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#define BEAST_DEFINE_HAS_MEMBER_FUNCTION(trait_name, member_function_name) \
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template<typename T, typename Signature> class trait_name; \
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\
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template<typename T, typename Result> \
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class trait_name<T, Result(void)> \
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{ \
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class yes { char m; }; \
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class no { yes m[2]; }; \
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struct base_mixin \
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{ \
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Result member_function_name(); \
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}; \
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struct base : public T, public base_mixin { private: base(); }; \
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template <typename U, U t> class helper{}; \
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template <typename U> \
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static no deduce(U*, helper<Result (base_mixin::*)(), &U::member_function_name>* = 0); \
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static yes deduce(...); \
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public: \
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static const bool value = sizeof(yes) == sizeof(deduce(static_cast<base*>(0))); \
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}; \
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\
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template<typename T, typename Result, typename Arg> \
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class trait_name<T, Result(Arg)> \
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{ \
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class yes { char m; }; \
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class no { yes m[2]; }; \
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struct base_mixin \
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{ \
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Result member_function_name(Arg); \
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}; \
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struct base : public T, public base_mixin { private: base(); }; \
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template <typename U, U t> class helper{}; \
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template <typename U> \
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static no deduce(U*, helper<Result (base_mixin::*)(Arg), &U::member_function_name>* = 0); \
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static yes deduce(...); \
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public: \
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static const bool value = sizeof(yes) == sizeof(deduce(static_cast<base*>(0))); \
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}; \
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\
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template<typename T, typename Result, typename Arg1, typename Arg2> \
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class trait_name<T, Result(Arg1,Arg2)> \
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{ \
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class yes { char m; }; \
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class no { yes m[2]; }; \
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struct base_mixin \
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{ \
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Result member_function_name(Arg1,Arg2); \
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}; \
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struct base : public T, public base_mixin { private: base(); }; \
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template <typename U, U t> class helper{}; \
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template <typename U> \
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static no deduce(U*, helper<Result (base_mixin::*)(Arg1,Arg2), &U::member_function_name>* = 0); \
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static yes deduce(...); \
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public: \
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static const bool value = sizeof(yes) == sizeof(deduce(static_cast<base*>(0))); \
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}; \
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\
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template<typename T, typename Result, typename Arg1, typename Arg2, typename Arg3> \
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class trait_name<T, Result(Arg1,Arg2,Arg3)> \
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{ \
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class yes { char m; }; \
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class no { yes m[2]; }; \
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struct base_mixin \
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{ \
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Result member_function_name(Arg1,Arg2,Arg3); \
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}; \
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struct base : public T, public base_mixin { private: base(); }; \
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template <typename U, U t> class helper{}; \
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template <typename U> \
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static no deduce(U*, helper<Result (base_mixin::*)(Arg1,Arg2,Arg3), &U::member_function_name>* = 0); \
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static yes deduce(...); \
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public: \
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static const bool value = sizeof(yes) == sizeof(deduce(static_cast<base*>(0))); \
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}; \
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\
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template<typename T, typename Result, typename Arg1, typename Arg2, typename Arg3, typename Arg4> \
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class trait_name<T, Result(Arg1,Arg2,Arg3,Arg4)> \
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{ \
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class yes { char m; }; \
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class no { yes m[2]; }; \
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struct base_mixin \
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{ \
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Result member_function_name(Arg1,Arg2,Arg3,Arg4); \
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}; \
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struct base : public T, public base_mixin { private: base(); }; \
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template <typename U, U t> class helper{}; \
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template <typename U> \
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static no deduce(U*, helper<Result (base_mixin::*)(Arg1,Arg2,Arg3,Arg4), &U::member_function_name>* = 0); \
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static yes deduce(...); \
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public: \
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static const bool value = sizeof(yes) == sizeof(deduce(static_cast<base*>(0))); \
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}
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#define BEAST_DEFINE_IS_CALL_POSSIBLE(trait_name, member_function_name) \
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struct trait_name##_detail \
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{ \
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BEAST_DEFINE_HAS_MEMBER_FUNCTION(has_member, member_function_name); \
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}; \
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\
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template <typename T, typename Signature> \
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struct trait_name \
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{ \
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private: \
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class yes {}; \
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class no { yes m[2]; }; \
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struct derived : public T \
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{ \
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using T::member_function_name; \
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no member_function_name(...) const; \
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private: derived (); \
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}; \
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\
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typedef typename is_call_possible_detail::clone_constness<T, derived>::type derived_type; \
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\
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template <typename U, typename Result> \
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struct return_value_check \
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{ \
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static yes deduce(Result); \
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static no deduce(...); \
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static no deduce(no); \
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static no deduce(is_call_possible_detail::void_exp_result<T>); \
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}; \
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\
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template <typename U> \
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struct return_value_check<U, void> \
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{ \
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static yes deduce(...); \
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static no deduce(no); \
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}; \
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\
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template <bool has_the_member_of_interest, typename F> \
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struct impl \
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{ \
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static const bool value = false; \
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}; \
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\
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template <typename Result, typename Arg> \
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struct impl<true, Result(Arg)> \
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{ \
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static typename is_call_possible_detail::add_reference<derived_type>::type test_me; \
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static typename is_call_possible_detail::add_reference<Arg>::type arg; \
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\
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static const bool value = \
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sizeof( \
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return_value_check<T, Result>::deduce( \
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(test_me.member_function_name(arg), is_call_possible_detail::void_exp_result<T>()) \
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) \
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) == sizeof(yes); \
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}; \
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\
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template <typename Result, typename Arg1, typename Arg2> \
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struct impl<true, Result(Arg1,Arg2)> \
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{ \
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static typename is_call_possible_detail::add_reference<derived_type>::type test_me; \
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static typename is_call_possible_detail::add_reference<Arg1>::type arg1; \
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static typename is_call_possible_detail::add_reference<Arg2>::type arg2; \
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\
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static const bool value = \
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sizeof( \
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return_value_check<T, Result>::deduce( \
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(test_me.member_function_name(arg1,arg2), is_call_possible_detail::void_exp_result<T>()) \
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) \
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) == sizeof(yes); \
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}; \
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\
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template <typename Result, typename Arg1, typename Arg2, typename Arg3> \
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struct impl<true, Result(Arg1,Arg2,Arg3)> \
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{ \
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static typename is_call_possible_detail::add_reference<derived_type>::type test_me; \
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static typename is_call_possible_detail::add_reference<Arg1>::type arg1; \
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static typename is_call_possible_detail::add_reference<Arg2>::type arg2; \
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static typename is_call_possible_detail::add_reference<Arg3>::type arg3; \
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\
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static const bool value = \
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sizeof( \
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return_value_check<T, Result>::deduce( \
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(test_me.member_function_name(arg1,arg2,arg3), is_call_possible_detail::void_exp_result<T>()) \
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) \
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) == sizeof(yes); \
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}; \
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\
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template <typename Result, typename Arg1, typename Arg2, typename Arg3, typename Arg4> \
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struct impl<true, Result(Arg1,Arg2,Arg3,Arg4)> \
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{ \
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static typename is_call_possible_detail::add_reference<derived_type>::type test_me; \
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static typename is_call_possible_detail::add_reference<Arg1>::type arg1; \
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static typename is_call_possible_detail::add_reference<Arg2>::type arg2; \
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static typename is_call_possible_detail::add_reference<Arg3>::type arg3; \
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static typename is_call_possible_detail::add_reference<Arg4>::type arg4; \
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\
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static const bool value = \
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sizeof( \
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return_value_check<T, Result>::deduce( \
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(test_me.member_function_name(arg1,arg2,arg3,arg4), is_call_possible_detail::void_exp_result<T>()) \
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) \
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) == sizeof(yes); \
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}; \
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\
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public: \
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static const bool value = impl<trait_name##_detail::has_member<T,Signature>::value, Signature>::value; \
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}
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//------------------------------------------------------------------------------
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/* Brings functional support into our namespace, based on environment.
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