id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
6454	Problem when using phoenix::_if with boost::optional in Spirit	Öyvind Strand <oyvind.strand@…>	Thomas Heller	"A rule that yields a boost::optional as attribute won't compile when using qi::_1 as condition for phoenix::_if.
However, if you add a phoenix statement after the if_ statement the rule compiles.

  //Doesn't compile
  qi::rule<Iter, boost::optional<int>()> rule_a = 
    (-qi::int_)[
      phx::if_(qi::_1)[
        phx::nothing
      ]
      //Uncomment next line and it compiles
      // , phx::nothing
    ]
 ;

It doesn't help if you use another operator than -

  //Doesn't compile
  qi::rule<Iter, boost::optional< boost::variant<int, double> >() > rule_b =
    (qi::int_ | qi::double_ | qi::eps)[
      phx::if_(qi::_1)[
        phx::nothing
      ]
      //Uncomment next line and it compiles
      // , phx::nothing
    ]
  ;

The error doesn't manifest if you don't refer to qi::_1

  //Compiles
  qi::rule<Iter, boost::optional< boost::variant<int, double> >() > rule_c =
    (qi::int_ | qi::double_ | qi::eps)[
      phx::if_(phx::val(true))[
        phx::nothing
      ]
    ]
  ;

It also works if you refer to qi::_1 but don't use phoenix::if_

  //Compiles
  qi::rule<Iter, boost::optional<int>()> rule_d = 
    (-qi::int_)[
      std::cout << qi::_1
    ]
  ;

Doing the same thing as in rule_a and rule_b outside of Spirit semantic actions also works

  //Compiles
  phx::if_(arg1)[
    phx::nothing
  ]
  (boost::optional<int>(5));

The problem doesn't seem to occur when using Phoenix v2 only v3"	Bugs	new	To Be Determined	phoenix	Boost Development Trunk	Problem