Added support of String class (issue #55, #56, #70, #77)

include/ArduinoJson/JsonObjectKey.hpp

@@ -0,0 +1,24 @@
+// Copyright Benoit Blanchon 2014-2015
+// MIT License
+//
+// Arduino JSON library
+// https://github.com/bblanchon/ArduinoJson
+
+#pragma once
+
+#include "Arduino/String.hpp"
+
+namespace ArduinoJson {
+
+class JsonObjectKey {
+ public:
+  JsonObjectKey() {}
+  JsonObjectKey(const char* key) : _data(key) {}
+  JsonObjectKey(const String& key) : _data(key.c_str()) {}
+
+  operator const char*() const { return _data; }
+
+ private:
+  const char* _data;
+};
+}