Re: [boost] [log][phoenix] Bound arguments not protoified?

Subject: Re: [boost] [log][phoenix] Bound arguments not protoified?
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-02-06 02:17:13

On Sat, Feb 2, 2013 at 8:26 PM, Andrey Semashev
<andrey.semashev_at_[hidden]> wrote:
> Hi,
>
> 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:
>
> 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);
>
> // The function initializes the logging library
> void init_logging()
> {
>   // ...
>   sink->set_formatter
>   (
>     expr::stream
>       << phoenix::bind(&severity_level_as_urgency, logging::trivial::severity)
>   );
> }
>
> The intended behavior of this code is to invoke severity_level_as_urgency
> function with severity level value extracted from a log record and put the
> result of this function into a stream, thus forming a formatted representation
> of the record.
>
> 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 posted in the end of the post.
>
> 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. Is that right?
>
> In case if you want to see the complete code of the example and/or Boost.Log,
> you can check it out from SVN:
>
> svn co https://boost-log.svn.sourceforge.net/svnroot/boost-
> log/branches/bleeding-edge boost-log
>
> The example resides in libs/log/example/doc/extension_app_launcher.cpp. I have
> modified it to call or_none() on trivial::severity so that the example
> compiles; in order to reproduce the problem you have to remove this call (it
> sould be performed by my protoify specialization instead).

Ping? Anyone? Should I create a ticket for Boost.Phoenix?