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copied!<p>For clarity - the error here is that <code>base_ >> int_ >> int_</code> was used as the expression for a rule that creates a <code>myderived</code>, and since <code>base_</code> is fixed to type <code>mybase</code>, we'd have to create a <code>myderrived</code> from a <code>mybase</code> and two <code>int</code>s, but there's nothing to tell Spirit how to do that.</p> <p>You can get boost to print out the type of the value that boost creates from parsing <code>base_ >> int_ >> int_</code> by defining a functor that will take any parameters, and tell you what they are (the following code is adapted from some code sehe put on SO chat): </p> <pre><code>struct what_is_the_attr { template <typename> struct result { typedef bool type; }; template <typename T> static void print_the_type() { std::cout << " "; std::cout << typeid(T).name(); if(std::is_const<typename std::remove_reference<T>::type>::value) std::cout << " const"; if(std::is_rvalue_reference<T>::value) std::cout << " &&"; else if(std::is_lvalue_reference<T>::value) std::cout << " &"; } template <typename Th, typename Th2, typename... Tt> static void print_the_type() { print_the_type<Th>(); std::cout << ",\n"; print_the_type<Th2, Tt...>(); } template <typename... Ts> void operator()(Ts&&...) const { std::cout << "what_is_the_attr(\n"; print_the_type<Ts...>(); std::cout << ")" << std::endl; } }; </code></pre> <p>Then to use it, use the above actor in a semantic action on initializer for your faulty rule:</p> <pre><code>std::string input = "1 2 3 4"; auto f(std::begin(input)), l(std::end(input)); rule<decltype(f), mybase() , space_type> base_ = int_ >> int_; rule<decltype(f), myderived(), space_type> derived_ = (base_ >> int_ >> int_)[what_is_the_attr()]; myderived data; bool ok = phrase_parse(f,l,derived_,space,data); </code></pre> <p><em>Note, you cannot use automatic attribute propagation with <code>%=</code> (unless you remove the exposed attribute type from the rule's declared type).</em></p> <p>Running this should then yield an encoded type, which can be decoded with <code>c++filt -t</code>: <strong><a href="http://coliru.stacked-crooked.com/a/4f5c90240b96d037" rel="nofollow">Live On Coliru</a></strong></p> <pre><code>$ g++ 9404189.cpp -std=c++0x $ ./a.out |c++filt -t what_is_the_attr( boost::fusion::vector3<mybase, int, int> &, boost::spirit::context<boost::fusion::cons<boost::spirit::unused_type&, boost::fusion::nil>, boost::fusion::vector0<void> > &, bool &) </code></pre> <p>The first line, <code>boost::fusion::vector3<mybase, int, int></code>, least tells you that boost is trying to create your return type from 3 objects of types <code>mybase</code>, <code>int</code> and <code>int</code>.</p>

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