Merge pull request #795 from jseward/develop

Add transparent comparator and perfect forwarding support to find() and count()

src/json.hpp

@@ -109,6 +109,14 @@ SOFTWARE.
     #define JSON_UNLIKELY(x)    x
 #endif
 
+// cpp language standard detection
+#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+    #define JSON_HAS_CPP_17
+    #define JSON_HAS_CPP_14
+#elif (defined(__cplusplus) && __cplusplus >= 201402L) || (defined(_HAS_CXX14) && _HAS_CXX14 == 1)
+    #define JSON_HAS_CPP_14
+#endif
+
 /*!
 @brief namespace for Niels Lohmann
 @see https://github.com/nlohmann
@@ -7566,9 +7574,17 @@ class basic_json
     7159](http://rfc7159.net/rfc7159), because any order implements the
     specified "unordered" nature of JSON objects.
     */
+
+#if defined(JSON_HAS_CPP_14)
+    // Use transparent comparator if possible, combined with perfect forwarding
+    // on find() and count() calls prevents unnecessary string construction.
+    using object_comparator_t = std::less<>;
+#else
+    using object_comparator_t = std::less<StringType>;
+#endif
     using object_t = ObjectType<StringType,
           basic_json,
-          std::less<StringType>,
+          object_comparator_t,
           AllocatorType<std::pair<const StringType,
           basic_json>>>;
 
@@ -9819,7 +9835,7 @@ class basic_json
 #ifndef _MSC_VER  // fix for issue #167 operator<< ambiguity under VS2015
                    and not std::is_same<ValueType, std::initializer_list<typename string_t::value_type>>::value
 #endif
-#if (defined(__cplusplus) && __cplusplus >= 201703L) || (defined(_MSC_VER) && _MSC_VER >1900 && defined(_HAS_CXX17) && _HAS_CXX17 == 1) // fix for issue #464
+#if defined(JSON_HAS_CPP_17)
                    and not std::is_same<ValueType, typename std::string_view>::value
 #endif
                    , int >::type = 0 >
@@ -10845,7 +10861,7 @@ class basic_json
     @note This method always returns @ref end() when executed on a JSON type
           that is not an object.
 
-    @param[in] key key value of the element to search for
+    @param[in] key key value of the element to search for.
 
     @return Iterator to an element with key equivalent to @a key. If no such
     element is found or the JSON value is not an object, past-the-end (see
@@ -10857,13 +10873,14 @@ class basic_json
 
     @since version 1.0.0
     */
-    iterator find(typename object_t::key_type key)
+    template<typename KeyT>
+    iterator find(KeyT&& key)
     {
         auto result = end();
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_value.object->find(key);
+            result.m_it.object_iterator = m_value.object->find(std::forward<KeyT>(key));
         }
 
         return result;
@@ -10871,15 +10888,16 @@ class basic_json
 
     /*!
     @brief find an element in a JSON object
-    @copydoc find(typename object_t::key_type)
+    @copydoc find(KeyT&&)
     */
-    const_iterator find(typename object_t::key_type key) const
+    template<typename KeyT>
+    const_iterator find(KeyT&& key) const
     {
         auto result = cend();
 
         if (is_object())
         {
-            result.m_it.object_iterator = m_value.object->find(key);
+            result.m_it.object_iterator = m_value.object->find(std::forward<KeyT>(key));
         }
 
         return result;
@@ -10906,10 +10924,11 @@ class basic_json
 
     @since version 1.0.0
     */
-    size_type count(typename object_t::key_type key) const
+    template<typename KeyT>
+    size_type count(KeyT&& key) const
     {
         // return 0 for all nonobject types
-        return is_object() ? m_value.object->count(key) : 0;
+        return is_object() ? m_value.object->count(std::forward<KeyT>(key)) : 0;
     }
 
     /// @}