add a macro for has_xxx types

nlohmann · Nov 18, 2016 · d9a7493 · d9a7493
1 parent e23bb39
commit d9a7493
Showing 1 changed file with 17 additions and 49 deletions.
diff --git a/src/json.hpp b/src/json.hpp
@@ -144,57 +144,25 @@ namespace nlohmann
   @sa http://stackoverflow.com/a/7728728/266378
   @since version 1.0.0, overworked in version 2.0.6
   */
-  template <typename T> struct has_mapped_type
-  {
-  private:
-    template <typename U, typename = typename U::mapped_type>
-    static int detect(U &&);
-
-    static void detect(...);
-
-  public:
-    static constexpr bool value =
-        std::is_integral<decltype(detect(std::declval<T>()))>::value;
-    };
-
-    template<typename T>
-    struct has_key_type
-    {
-    private:
-      template <typename U, typename = typename U::key_type>
-      static int detect(U&&);
-
-      static void detect(...);
-    public:
-      static constexpr bool value =
-        std::is_integral<decltype(detect(std::declval<T>()))>::value;
-    };
-
-    template<typename T>
-    struct has_value_type
-    {
-    private:
-      template <typename U, typename = typename U::value_type>
-      static int detect(U&&);
-
-      static void detect(...);
-    public:
-      static constexpr bool value =
-        std::is_integral<decltype(detect(std::declval<T>()))>::value;
-    };
+#define NLOHMANN_JSON_HAS_HELPER(type)                                         \
+  template <typename T> struct has_##type {                                    \
+  private:                                                                     \
+    template <typename U, typename = typename U::type>                         \
+    static int detect(U &&);                                                   \
+                                                                               \
+    static void detect(...);                                                   \
+                                                                               \
+  public:                                                                      \
+    static constexpr bool value =                                              \
+        std::is_integral<decltype(detect(std::declval<T>()))>::value;          \
+  };
 
-    template<typename T>
-    struct has_iterator
-    {
-    private:
-      template <typename U, typename = typename U::iterator>
-      static int detect(U&&);
+NLOHMANN_JSON_HAS_HELPER(mapped_type)
+NLOHMANN_JSON_HAS_HELPER(key_type)
+NLOHMANN_JSON_HAS_HELPER(value_type)
+NLOHMANN_JSON_HAS_HELPER(iterator)
 
-      static void detect(...);
-    public:
-      static constexpr bool value =
-        std::is_integral<decltype(detect(std::declval<T>()))>::value;
-    };
+#undef NLOHMANN_JSON_HAS_HELPER
 
     template <bool B, class RealType, class CompatibleObjectType>
     struct is_compatible_object_type_impl : std::false_type {};