Re: [Boost-bugs] [Boost C++ Libraries] #5588: property_tree INFO include directive

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #5588: property_tree INFO include directive
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-12-01 23:02:44

#5588: property_tree INFO include directive
---------------------------------+------------------------------------------
  Reporter:  sarum9in@…          |       Owner:  cornedbee    
      Type:  Bugs                |      Status:  new          
 Milestone:  To Be Determined    |   Component:  property_tree
   Version:  Boost 1.46.1        |    Severity:  Problem      
Resolution:                      |    Keywords:               
---------------------------------+------------------------------------------

Comment (by Filippov Aleksey <sarum9in@…>):

 While I was changing current implementation I went to the following
 architecture:

 We can implement event-like class that will receive the following events:
 enter(std::string) and exit(),
 also this class will provide a query method: resolve(std::string) ->
 std::string.

 We can use this in the following way: let's introduce new template
 argument to every read_info function named PathResolver.
 Such functions will accept PathResolver instances as their last argument:

 {{{
 template<class Ptree, class Ch, class PathResolver>
 void read_info(std::basic_istream<Ch> &stream, Ptree &pt,
                PathResolver &path_resolver)
 {
     //...
 }
 }}}

 We should also provide overloads with old interface for every such
 read_info function:
 {{{
 template<class Ptree, class Ch>
 void read_info(std::basic_istream<Ch> &stream, Ptree &pt)
 {
         default_path_resolver pr;
         read_info(stream, pt, pr);
 }
 }}}

 Let's reimplement read_info_internal in the following way:
 {{{
 template<class Ptree, class Ch, class PathResolver>
 void read_info_internal(std::basic_istream<Ch> &stream,
                         Ptree &pt,
                         const std::string &filename,
                         PathResolver &path_resolver,
                         int include_depth)
 {
     //...
     std::basic_ifstream<Ch> inc_stream(
         path_resolver.resolve(inc_name.c_str()));
     //...
     path_resolver.enter(inc_name);
     read_info_internal(/*...*/);
     path_resolver.exit();
     //...
 }
 }}}

 There is a case when we do not know the real file name, for example if
 user passes std::istream-like object. In that case PathResolver has to
 implement enter() method (without arguments).

 As you has noticed, I used non-const references in code. In my opinion it
 should be done in that way because PathResolver can have inner state.
 It is much simplier and efficientlier to pass object by reference rather
 than implementing inner share-state for (PathResolver path_resolver)
 signature
 or (const PathResolver &path_resolver) one. Please note, that my changes
 will not break any legacy code. I have provided old-style
 overloads with default_path_resolver.

 I do not think this changes are completed. I tried to show you only idea.
 My code is still
 unchecked and probably have bugs.

 One question I have: how user should access standard path resolvers?
 Should we export them like read_info functions to boost::property_tree
 namespace?
 Or should we do something else?

 P.S.
 In my opinion publishing code that is being at developing stage only to
 bugtracker is not a good idea.
 I have created public git repository to share my code, if you can't watch
 it through git, I have created a patch.

 git repository is located at
 [http://cs.istu.ru/gitweb/?p=boost.git;a=summary].

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/5588#comment:4>
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