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    copied!<p>Some time has passed, C++14 is being finalized, and compilers are adding support for new features, like generic lambdas.</p> <p>Generic lambdas, together with the machinery shown below, allow achieving the desired (dynamic) polymorphism with unrelated classes:</p> <pre><code>#include &lt;boost/variant.hpp&gt; template&lt;typename R, typename F&gt; class delegating_visitor : public boost::static_visitor&lt;R&gt; { public: delegating_visitor(F&amp;&amp; f) : _f(std::forward&lt;F&gt;(f)) { } template&lt;typename T&gt; R operator () (T x) { return _f(x); } private: F _f; }; template&lt;typename R, typename F&gt; auto make_visitor(F&amp;&amp; f) { using visitor_type = delegating_visitor&lt;R, std::remove_reference_t&lt;F&gt;&gt;; return visitor_type(std::forward&lt;F&gt;(f)); } template&lt;typename R, typename V, typename F&gt; auto vcall(V&amp;&amp; vt, F&amp;&amp; f) { auto v = make_visitor&lt;R&gt;(std::forward&lt;F&gt;(f)); return vt.apply_visitor(v); } #define call_on_variant(val, fxn_expr) \ vcall&lt;int&gt;(val, [] (auto x) { return x-&gt; fxn_expr; }); </code></pre> <p>Let's put this into practice. Supposing to have the following two unrelated classes:</p> <pre><code>#include &lt;iostream&gt; #include &lt;string&gt; struct A { int foo(int i, double d, std::string s) const { std::cout &lt;&lt; "A::foo(" &lt;&lt; i &lt;&lt; ", " &lt;&lt; d &lt;&lt; ", " &lt;&lt; s &lt;&lt; ")"; return 1; } }; struct B { int foo(int i, double d, std::string s) const { std::cout &lt;&lt; "B::foo(" &lt;&lt; i &lt;&lt; ", " &lt;&lt; d &lt;&lt; ", " &lt;&lt; s &lt;&lt; ")"; return 2; } }; </code></pre> <p>It is possible to invoke <code>foo()</code> polymorphically this way:</p> <pre><code>int main() { A a; B b; boost::variant&lt;A*, B*&gt; v = &amp;a; auto res1 = call_on_variant(v, foo(42, 3.14, "Hello")); std::cout &lt;&lt; std::endl&lt;&lt; res1 &lt;&lt; std::endl; v = &amp;b; auto res2 = call_on_variant(v, foo(1337, 6.28, "World")); std::cout &lt;&lt; std::endl&lt;&lt; res2 &lt;&lt; std::endl; } </code></pre> <p>And the output is, as expected:</p> <pre><code>A::foo(42, 3.14, Hello) 1 B::foo(1337, 6.28, World) 2 </code></pre> <p>The program has been tested on VC12 with November 2013's CTP. Unfortunately, I do not know of any online compiler that supports generic lambdas, so I cannot post a live example.</p>
 

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