delete undesired default members instead of making them inaccessible

unittest/force-styles/yaml_writer.h

@@ -22,6 +22,9 @@ class YamlWriter {
 public:
     YamlWriter(const char *outfile);
     virtual ~YamlWriter();
+    YamlWriter() = delete;
+    YamlWriter(const YamlWriter &) = delete;
+    const YamlWriter & operator=(const YamlWriter &) = delete;
 
     // emitters
     void emit(const std::string &key, const double value);
@@ -34,10 +37,6 @@ private:
     FILE *fp;
     yaml_emitter_t emitter;
     yaml_event_t event;
-
-private:
-    YamlWriter(){};
-    YamlWriter(const YamlWriter &){};
 };
 
 #endif