[Boost-users] [Solution] Re: [statechart] Template States, Compile Error

Hi Dave The problem you stumbled upon is (or was :-() well known. It was discussed during review and I even tried to find a workaround for it not too long ago. The solution is very simple and is even described in the reference manual under the requirements for the InnerInitial parameter: <quote> An mpl::list<> containing models of the SimpleState or State concepts or instantiations of the shallow_history or deep_history class templates. If there is only a single inner initial state _that_is_not_a_template_instantiation_ then it can also be passed directly, without wrapping it into an mpl::list<>. [...] </quote> (_Note_the_underlined_part_). So, the only thing you need to do is to wrap every templated InnerInitial parameter into an mpl::list and everything will work as expected (see attached example). The reason why compilers rightly choke on the code lies in the fact that simple_state internally checks whether the InnerInitial parameter already is an mpl::list. This check works perfectly even on forward-declared classes. However, as soon as InnerInitial is a class template instantiation, for some reason that template needs to be fully instantiated. The problem is described in more detail here: http://article.gmane.org/gmane.comp.lib.boost.devel/128741 I guess it was simply a little too late yesterday, sorry... #include #include #include namespace sc = boost::statechart; namespace mpl = boost::mpl; template< typename Type > struct NormalMode; struct Switch : sc::state_machine< Switch, NormalMode< int > > {}; template< typename Type > struct Off; template< typename Type > struct NormalMode : sc::simple_state< // Note that Off< Type > is wrapped into an mpl::list NormalMode< Type >, Switch, mpl::list< Off< Type > > > { }; template< typename Type > struct Off : sc::simple_state< Off< Type >, NormalMode< Type > > { }; int main() { Switch machine; machine.initiate(); return 0; } HTH, -- Andreas Huber When replying by private email, please remove the words spam and trap from the address shown in the header.