Merge pull request #324 from vpetrigo/has_mapped_improve

make has_mapped_type struct friendly

Merge pull request #324 from vpetrigo/has_mapped_improve
make has_mapped_type struct friendly
bb9d87ad · Niels Lohmann · GitHub · e7a60d89 · e9fde3e1 · bb9d87ad
Commit bb9d87ad authored Oct 12, 2016 by Niels Lohmann Committed by GitHub Oct 12, 2016
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Showing with 12 additions and 6 deletions

src/json.hpp src/json.hpp +6 -3

src/json.hpp.re2c src/json.hpp.re2c +6 -3

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--- a/src/json.hpp
+++ b/src/json.hpp
@@ -113,10 +113,13 @@ 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;
 };

 /*!

--- a/src/json.hpp.re2c
+++ b/src/json.hpp.re2c
@@ -113,10 +113,13 @@ 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;
 };

 /*!