From e9fde3e1166abb6ede4881c832c22d750e69e77b Mon Sep 17 00:00:00 2001
From: Vladimir Petrigo <taenaru@gmail.com>
Date: Sat, 8 Oct 2016 01:03:35 +0300
Subject: [PATCH] make has_mapped_type struct friendly

---
 src/json.hpp      | 9 ++++++---
 src/json.hpp.re2c | 9 ++++++---
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/json.hpp b/src/json.hpp
index 04c8573f..57fecf99 100644
--- a/src/json.hpp
+++ b/src/json.hpp
@@ -112,10 +112,13 @@ template<typename T>
 struct has_mapped_type
 {
   private:
-    template<typename C> static char test(typename C::mapped_type*);
-    template<typename C> static char (&test(...))[2];
+    template <typename U, typename = typename U::mapped_type>
+    static int detect(U&&);
+
+    static void detect(...);
   public:
-    static constexpr bool value = sizeof(test<T>(0)) == 1;
+    static constexpr bool value =
+        std::is_integral<decltype(detect(std::declval<T>()))>::value;
 };
 
 /*!
diff --git a/src/json.hpp.re2c b/src/json.hpp.re2c
index 48224835..e26ac7c7 100644
--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -112,10 +112,13 @@ template<typename T>
 struct has_mapped_type
 {
   private:
-    template<typename C> static char test(typename C::mapped_type*);
-    template<typename C> static char (&test(...))[2];
+    template <typename U, typename = typename U::mapped_type>
+    static int detect(U&&);
+
+    static void detect(...);
   public:
-    static constexpr bool value = sizeof(test<T>(0)) == 1;
+    static constexpr bool value =
+        std::is_integral<decltype(detect(std::declval<T>()))>::value;
 };
 
 /*!