c++ - Boost Spirit placeholder type conversion -


i'm trying write parser (as first step, of course expanded lot) parses double , creates object of class expressiontree passing double factory method of class. first try

struct operands : qi::grammar<string::iterator, expressiontree()>  {      operands() : operands::base_type(start)      {         start = qi::double_[qi::_val = expressiontree::number(qi::_1)];     }      qi::rule<string::iterator, expressiontree()> start;  };

this doesn't compile (can't convert boost::spirit::_1_type double) because (if understand correctly) qi::_1 not double evaluates double.

i tried using boost::bind(&expressiontree::number, _1) in way don't know how result assigned attribute _val

i grateful if point me in right direction.

you need lazy actors in semantic actions.

i'm assuming number static unary function or non-static nullary (instead of, e.g. type):

start = qi::double_ [ qi::_val = boost::phoenix::bind(&expressiontree::number, qi::_1)];

if type:

start = qi::double_ [ qi::_val = boost::phoenix::construct<expressiontree::number>(qi::_1)];

see also


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