Re: [Boost-bugs] [Boost C++ Libraries] #7495: Support for boost::optional in boost::program_options

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #7495: Support for boost::optional in boost::program_options
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-10-30 10:44:57

#7495: Support for boost::optional in boost::program_options
------------------------------------------+-----------------------------
  Reporter:  Dmitry Trifonov <user61a@…>  |      Owner:  vladimir_prus
      Type:  Feature Requests             |     Status:  new
 Milestone:  To Be Determined             |  Component:  program_options
   Version:  Boost 1.52.0                 |   Severity:  Optimization
Resolution:                               |   Keywords:
------------------------------------------+-----------------------------

Comment (by Edward Catmur <ed@…>):

 Implementing optional support via streaming would have unwanted side
 effects. The correct place to implement optional support is via the
 validate customization point:


 {{{
 namespace boost {

 template<class T>
 void validate(boost::any& v, std::vector<std::string> const& values,
 boost::optional<T>* typeTag, int)
 {
     if (!values.empty())
     {
         boost::any a;
         using namespace boost::program_options;
         validate(a, values, (T*)0, 0);
         v = boost::any(boost::optional<T>(boost::any_cast<T>(a)));
     }
 }

 }
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/7495#comment:5>
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