[Boost-bugs] [Boost C++ Libraries] #6454: Problem when using phoenix::_if with boost::optional in Spirit

Subject: [Boost-bugs] [Boost C++ Libraries] #6454: Problem when using phoenix::_if with boost::optional in Spirit
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-01-26 18:05:09

#6454: Problem when using phoenix::_if with boost::optional in Spirit
---------------------------------------------------+------------------------
 Reporter:  Öyvind Strand <oyvind.strand@…>        |       Owner:  theller
     Type:  Bugs                                   |      Status:  new    
Milestone:  To Be Determined                       |   Component:  phoenix
  Version:  Boost Development Trunk                |    Severity:  Problem
 Keywords:                                         |  
---------------------------------------------------+------------------------
 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

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6454>
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