Re: [Boost-bugs] [Boost C++ Libraries] #1132: zero_tokens doesn't work

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #1132: zero_tokens doesn't work
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-11-05 09:23:30

#1132: zero_tokens doesn't work
---------------------------------------------+------------------------------
 Reporter:  Bryan Green <bgreen0@…>          |       Owner:  vladimir_prus  
     Type:  Bugs                             |      Status:  new            
Milestone:  Boost 1.36.0                     |   Component:  program_options
  Version:  Boost 1.34.1                     |    Severity:  Problem        
 Keywords:                                   |  
---------------------------------------------+------------------------------

Comment(by vladimir_prus):

 Another way how zero_tokens is used to good effect is the 'bool_switch'
 function:

     BOOST_PROGRAM_OPTIONS_DECL typed_value<bool>*
     bool_switch(bool* v)
     {
         typed_value<bool>* r = new typed_value<bool>(v);
         r->default_value(0);
         r->zero_tokens();

         return r;
     }

 This, together with validator for the bool types, allows to make
 --whatever be interpreted as 'true' value for 'whatever' option. Note this
 code:

     BOOST_PROGRAM_OPTIONS_DECL void validate(any& v, const vector<string>&
 xs,
                        bool*, int)
     {
         check_first_occurrence(v);
         string s(get_single_string(xs, true));

 The 'true' passed to 'get_single_string' means that if there are no
 tokens, the empty string should be returned -- which is then interpreted
 as true value.

 Therefore, 'zero_tokens' makes sense exclusively when the validator for
 the type handles empty string or 'implied_value' is also specified. Seems
 like purely documentation bug to me, then.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/1132#comment:10>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.