Trying to return a reference to set from c++ to angelscript

[URGENT]Hi, straight to the point:

I have the following class method :

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Graph</span>
    {</span>
    <span class="hljs-keyword">const</span> <span class="hljs-built_in">std</span>::<span class="hljs-built_in">set</span><<span class="hljs-keyword">size_t</span>>&amp; get_selected_nodes() <span class="hljs-keyword">const</span>;
    …
    }

the following binding to angelscript:

engine->RegisterObjectType(<span class="hljs-string">"Graph"</span>, <span class="hljs-number">0</span>, asOBJ_REF);
engine->RegisterObjectMethod(<span class="hljs-string">"Graph"</span>, <span class="hljs-string">"set<uint>@ get_selected_nodes()"</span>, asMETHOD(gph::Graph, get_selected_nodes), asCALL_THISCALL);

engine->RegisterGlobalProperty("Graph g", g);

and i'm including …