Re: [Boost-bugs] [Boost C++ Libraries] #2429: raw[] attribute incompatibility

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #2429: raw[] attribute incompatibility
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-06-02 01:32:48

#2429: raw[] attribute incompatibility
------------------------------------------+---------------------------------
  Reporter:  vallentin_at_[hidden]  |       Owner:  djowel                       
      Type:  Bugs                         |      Status:  closed                       
 Milestone:  Boost 1.37.0                 |   Component:  spirit                       
   Version:  Boost 1.36.0                 |    Severity:  Problem                      
Resolution:  invalid                      |    Keywords:  raw, attribute, compatibility
------------------------------------------+---------------------------------
Changes (by hkaiser):

  * status:  new => closed
  * resolution:  => invalid

Comment:

 Replying to [ticket:2429 vallentin_at_[hidden]]:
 > I discovered an issue with the raw[] parser returning an
 iterator_range<T>.
 > While it should be compatible to std::string, it is not according to my
 > experience. Below, I attached an excerpt from the mailing list that
 captures the
 > problem pretty well.
 >
 > On Tue, Oct 21, 2008 at 09:04:48AM +0800, Joel de Guzman wrote:
 > > First, std::string should be compatible with iterator pair, so it
 should
 > > just be:
 > >
 > > raw["foo"][_val = _1]
 >
 > This was in fact my first choice but did not compile with several g++
 > versions [1]:

 This doesn't compile, and rightly so. _1 has the type iterator_range<> and
 _val has the type string. Since there is no assignment operator allowing
 to do this conversion, the compilation must fail. Everything ok so far.

 > > Or simply:
 > >
 > > r %= raw["foo"];
 >
 > Unlike the explicit above version, this works. This primarily drives my
 > confusion. However, in my more complex grammar I cannot use this
 > convenient approach.

 This must compile (and as you've seen, it does). The reason is, that the
 raw[] directive is able to store it's attribute in any type 'compatible'
 compatible with an iterator_range<>. That means it can store it's
 attribute in any type having a similar constructor as iterator_range (or
 otherwise similar conversion operators). As string has a constructor
 taking two iterators (as iterator_range<> does) the code above compiles
 and works fine.

 > > But, if you really need to get at the first/last, since
 > boost::iterator_range
 > > is a valid STL sequence, you can simply use:
 > >
 > > construct<std::string>(begin(_1),end(_1))
 > >
 > > begin and end are phoenix functions in the stl/container module.
 >
 > Interestingly replacing boost::phoenix::at_c<0>(_1) with begin(_1) /
 > end(_1) works and compiles.

 Remember spirit::arg_names::_1 is not the same as phoenix::_1. I hope this
 answers your question.

 Regards Hartmut

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/2429#comment:1>
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