From ba10f9bc94115aab1963039a44f914a2402ae06f Mon Sep 17 00:00:00 2001
From: Denis Mikhailov <denismikhaylov38@gmail.com>
Date: Wed, 20 Jul 2022 15:27:28 +0600
Subject: [PATCH] Update core14_classic.hpp

---
 include/boost/pfr/detail/core14_classic.hpp | 24 ++++++++++-----------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/include/boost/pfr/detail/core14_classic.hpp b/include/boost/pfr/detail/core14_classic.hpp
index a27d081..b8be1d3 100644
--- a/include/boost/pfr/detail/core14_classic.hpp
+++ b/include/boost/pfr/detail/core14_classic.hpp
@@ -599,13 +599,20 @@ struct ubiq_constructor_constexpr_copy {
 /////////////////////
 
 template <class T, std::size_t... I>
-struct is_constexpr_aggregate_initializable { // TODO: try to fix it
-    template <T = T{ ubiq_constructor_constexpr_copy{I}... } >
+struct is_constexpr_aggregate_initializable {
+    template<class T2, std::size_t... I2>
+    static constexpr void* constexpr_aggregate_initializer() {
+        const auto t = T2{ ubiq_constructor_constexpr_copy{I2}... };
+        (void)t;
+        return nullptr;
+    }
+
+    template <void* = constexpr_aggregate_initializer<T, I...>() >
     static std::true_type test(long) noexcept;
 
     static std::false_type test(...) noexcept;
 
-    static constexpr decltype( test(0) ) value{};
+    static constexpr bool value = decltype(test(0)){};
 };
 
 
@@ -676,16 +683,7 @@ void for_each_field_dispatcher(T& t, F&& f, std::index_sequence<I...>) {
         !std::is_union<T>::value,
         "====================> Boost.PFR: For safety reasons it is forbidden to reflect unions. See `Reflection of unions` section in the docs for more info."
     );
-
-    /// Compile time error at this point means that you have called `for_each_field` or some other non-flat function or operator for a
-    /// type that is not constexpr aggregate initializable.
-    ///
-    /// Make sure that all the fields of your type have constexpr default construtors and trivial destructors.
-    /// Or compile in C++17 mode.
-    constexpr T tmp{ ubiq_constructor_constexpr_copy{I}... };
-    (void)tmp;
-
-    //static_assert(is_constexpr_aggregate_initializable<T, I...>::value, "====================> Boost.PFR: T must be a constexpr initializable type");
+    static_assert(is_constexpr_aggregate_initializable<T, I...>::value, "====================> Boost.PFR: T must be a constexpr initializable type");
 
     constexpr bool is_flat_refelectable_val = detail::is_flat_refelectable<T>( std::index_sequence<I...>{} );
     detail::for_each_field_dispatcher_1(