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POvisitor pattern for boost::any
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  1. POvisitor pattern for boost::any
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    copied!<p>I found this <a href="https://gist.github.com/2945472">https://gist.github.com/2945472</a> but I need an implementation that does not depend on c++11. I tried my hand at converting it to use only boost, but I'm having some trouble.</p> <p>Here is what I came up with:</p> <pre><code>#include &lt;boost/any.hpp&gt; #include &lt;boost/function.hpp&gt; #include &lt;boost/bind.hpp&gt; #include &lt;boost/lambda/lambda.hpp&gt; #include &lt;boost/unordered_map.hpp&gt; struct type_info_hash { std::size_t operator()(std::type_info const &amp; t) const { return t.hash_code(); } }; struct equal_ref { template &lt;typename T&gt; bool operator()(boost::reference_wrapper&lt;T&gt; a,boost::reference_wrapper&lt;T&gt; b) const { return a.get() == b.get(); } }; struct any_visitor { boost::unordered_map&lt;boost::reference_wrapper&lt;std::type_info const&gt;, boost::function&lt;void(boost::any&amp;)&gt;, type_info_hash, equal_ref&gt; fs; template &lt;typename T&gt; void insert_visitor(boost::function&lt;void(T)&gt; f) { try { fs.insert(std::make_pair(boost::ref(typeid(T)), boost::bind(f, boost::any_cast&lt;T&gt;(boost::lambda::_1)))); } catch (boost::bad_any_cast&amp; e) { std::cout &lt;&lt; e.what() &lt;&lt; std::endl; } } bool operator()(boost::any &amp; x) { boost::unordered_map&lt;boost::reference_wrapper&lt;std::type_info const&gt;, boost::function&lt;void(boost::any&amp;)&gt;, type_info_hash, equal_ref&gt;::iterator it = fs.find(boost::ref(x.type())); if (it != fs.end()) { it-&gt;second(x); return true; } else { return false; } } }; struct abc {}; void fa(int i) { std::cout &lt;&lt; "fa(" &lt;&lt; i &lt;&lt; ")" &lt;&lt; std::endl; } void fb(abc) { std::cout &lt;&lt; "fb(abc())" &lt;&lt; std::endl; } int main() { any_visitor f; f.insert_visitor&lt;int&gt;(fa); f.insert_visitor&lt;abc&gt;(fb); std::vector&lt;boost::any&gt; xs; xs.push_back(1); xs.push_back(abc()); xs.push_back(1.5); for (auto &amp; x : xs) { if (!f(x)) std::cout &lt;&lt; "no visitor registered" &lt;&lt; std::endl; } } </code></pre> <p>I'm getting a bad_any_cast when inserting into the map. Shouldn't any_cast only be called by it->second(x) ? What am I doing wrong?</p>
 

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