Re: [Boost-bugs] [Boost C++ Libraries] #6043: Spirit insists that user types are adapted to Fusion

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6043: Spirit insists that user types are adapted to Fusion
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-11-09 00:16:15

#6043: Spirit insists that user types are adapted to Fusion
-------------------------------+--------------------------------------------
  Reporter:  vladimir_prus     |       Owner:  djowel 
      Type:  Patches           |      Status:  new    
 Milestone:  To Be Determined  |   Component:  spirit 
   Version:  Boost 1.47.0      |    Severity:  Problem
Resolution:                    |    Keywords:         
-------------------------------+--------------------------------------------

Comment (by anonymous):

 Here's what's happening:

 When you have A >> B, the rules are: http://tinyurl.com/bqch2m6


 So, as far as compatibility goes, the attribute either has to be a fusion
 sequence *or* a std container. That is why your code does not compile.

 The thing is, spirit is optimal and walks the sequence and builds its
 elements in-situ, instead of synthesising a temporary sequence in memory
 and assign later. That is why it has to iterate over existing instances.
 In this case, it cannot walk a foo. Heller's workaround works because the
 inner rule is able to walk the fusion sequence and then attribute
 transformation kicks in whereby it assigns the fusion sequence to foo.
 That works but is sub optimal.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6043#comment:3>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.