[Boost-bugs] [Boost C++ Libraries] #7996: phoenix::bind does not protoify the bound arguments

Subject: [Boost-bugs] [Boost C++ Libraries] #7996: phoenix::bind does not protoify the bound arguments
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-02-06 18:10:14

#7996: phoenix::bind does not protoify the bound arguments
------------------------------------+---------------------------------------
 Reporter:  andysem                 |       Owner:  theller
     Type:  Bugs                    |      Status:  new    
Milestone:  To Be Determined        |   Component:  phoenix
  Version:  Boost Release Branch    |    Severity:  Problem
 Keywords:  phoenix bind proto log  |  
------------------------------------+---------------------------------------
 I have a problem with Boost.Phoenix v3 bind implementation when used with
 attribute keywords from Boost.Log. For some reason phoenix::bind does not
 apply proto::detail::protoify to the bound arguments which breaks
 compilation of some formatting expressions in Boost.Log.

 Here's an example:

 {{{
 #include <boost/phoenix.hpp>
 #include <boost/log/trivial.hpp>
 #include <boost/log/expressions.hpp>
 #include <boost/log/utility/value_ref.hpp>

 namespace logging = boost::log;
 namespace expr = boost::log::expressions;
 namespace phoenix = boost::phoenix;

 // Custom severity level formatting function
 std::string severity_level_as_urgency(
     logging::value_ref< logging::trivial::severity_level,
 logging::trivial::tag::severity > const& level)
 {
     if (!level || level.get() == logging::trivial::info)
         return "normal";
     logging::trivial::severity_level lvl = level.get();
     if (lvl < logging::trivial::info)
         return "low";
     else
         return "critical";
 }

 int main(int, char*[])
 {
     logging::formatter fmt =
         expr::stream << boost::phoenix::bind(&severity_level_as_urgency,
 logging::trivial::severity);

     return 0;
 }
 }}}

 The example creates a formatter function object that should call
 severity_level_as_urgency function to convert the severity level to string
 and put its result into a stream.

 trivial::severity is a keyword of type expr::attribute_keyword< ... >.
 Keywords themselves should never actually be embedded into phoenix
 expressions, instead I have attribute_actor that implements all the
 necessary work to extract attribute values. I have specialized
 proto::detail::protoify template for attribute_keyword (including
 references and reference_wrappers thereof) so that it is automatically
 converted to attribute_actor whenever it participates in expressions. But
 it doesn't work with the above code, Boost.Phoenix embeds
 attribute_keyword as is into the expression. This results
 in the error I attached to the ticket.

 I realize that proto::detail::protoify is not for public use and may not
 be intended for my use case but I did not find any other way to implement
 what I described. Anyway, I think bind should treat bound arguments as
 child subexpressions and protoify them.

 To compile the test code you will have to checkout Boost.Log from SVN:

 {{{
 svn co https://boost-log.svn.sourceforge.net/svnroot/boost-log/branches

 /bleeding-edge -r 822 boost-log
 }}}

 Then the relevant directories have to be linked/copied into the Boost
 tree.


 PS: The issue came from the mailing list:

 [http://lists.boost.org/Archives/boost/2013/02/200701.php]

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7996>
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