Re: [Boost-users] [Spirit/Qi/Phoenix] non compiling rules...

Subject: Re: [Boost-users] [Spirit/Qi/Phoenix] non compiling rules...
From: TONGARI J (tongari95_at_[hidden])
Date: 2013-12-12 09:24:33

2013/12/12 Francois Mauger <mauger_at_[hidden]>

> Dear Boosters,
>
> The following code is one of my first attempts to use Spirit/Qi.
> For my education, I have tried 2 techniques to parse the simple "aaa=131;"
> string.
> The first one (Block A) compiles and seems to output the expected result.
> The second (B) does not compile with a huge massively templatized
> backtrace that I don't understand.
> What is the difference between using online rules and
> rule objects ? Is there a syntax error somewhere ?
> I'm afraid the documentation and example are rather terse about the
> syntax to be used here  when coupling Qi and Phoenix...
>

[snip]

>     boost::spirit::qi::rule<std::string::iterator> key_rule   = +(char_ -
> '=');
>     boost::spirit::qi::rule<std::string::iterator> value_rule =
> lexeme[+(char_ - ';')];
>
>     bool r = phrase_parse(
>                           strbegin,
>                           s.end(),
>                           key_rule[boost::phoenix::ref(vkey) =
> boost::spirit::qi::_1 ]   // <----HERE
>                           >> '=' >> *space
>                           >> value_rule[boost::phoenix::ref(vvalue) =
> boost::spirit::qi::_1 ],   // <----HERE
>                           space
>                           );
>

The problem is (at least what I see): your key_rule/value_rule have no
attribute, so qi::_1 eventually evaluates to nothing (i.e. unused_type).
To give them attr, for example:

    boost::spirit::qi::rule<std::string::iterator, std::vector<char>()>
key_rule;

And I'd suggest using attr propagation instead of the explicit semantic
action if possible.

HTH