Updated v2_0_cpp_adaptor (markdown)

v2_0_cpp_adaptor.md

@@ -282,6 +282,45 @@ struct object_with_zone<my_class> {
 
 https://github.com/msgpack/msgpack-c/blob/master/example/cpp03/class_non_intrusive.cpp
 
+When you use `msgpack::object::as` member function template in `convert` class template specilization, , temporary objects are created.
+
+```C++
+template<>
+struct convert<my_class> {
+    msgpack::object const& operator()(msgpack::object const& o, my_class& v) const {
+        if (o.type != msgpack::type::ARRAY) throw msgpack::type_error();
+        if (o.via.array.size != 2) throw msgpack::type_error();
+        v = my_class(
+            o.via.array.ptr[0].as<std::string>(), // temporary object is created here
+            o.via.array.ptr[1].as<int>());
+        return o;
+    }
+};
+```
+
+If you can get the reference of the member variables in converting target class, you can remove the temporary object creation. For example, if member variables of `my_class` are public, you can apply `operator>>` to them as follows:
+
+```C++
+class my_class {
+public:
+    /* ... */
+    std::string name_;
+    int age_;
+};
+
+template<>
+struct convert<my_class> {
+    msgpack::object const& operator()(msgpack::object const& o, my_class& v) const {
+        if (o.type != msgpack::type::ARRAY) throw msgpack::type_error();
+        if (o.via.array.size != 2) throw msgpack::type_error();
+        o.via.array.ptr[0] >> v.name_; // no temporary object creation
+        o.via.array.ptr[1] >> v.age_;
+        return o;
+    }
+};
+```
+
+
 #### non default constructible class support (C++11 only, since 1.2.0)
 You might want to convert to a class that doesn't have default constructor from a msgpack::object. In order to do that, you can use 'as' class template specialization.