Re: [boost] boost::gregorian::date_period, how to increment/decrement the period

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-03-26 15:22:52

On Sun, 26 Mar 2006 19:19:44 +0000 (UTC), george wrote
> hello!
> 
> boost::gregorian::days size(1);
> 
> boost::gregorian::date_period tmp(period.begin()+=size,period.end()
> -=size);
> 
> period=tmp;
> 
> is there any better way to increment/decrement the period object
> 
> I want 
> period.begin+=size;
> period.end()-=size
> 
> to be permanent to period but it doesn't,it returns an object...
> 
> any idea??

No there isn't an easy way to do this in the current release.  However, I've
checked in a new function to boost/date_time/period.hpp called 'expand' which
provides this capability.

So you can now say:

date_period dp(.....);
dp.expand(days(2));

Of course, due to the wonders of generic programming this will now work for
time periods too :-)

time_period tp(.....);
tp.expand(minutes(10));

You can easily patch it in yourself or download a new period.hpp from cvs. 
Basically in the period.hpp file add this:

  template<class point_rep, class duration_rep>
  class period : private
  //....
    void expand(const duration_rep& d);
  //...

Then later in the file 

  /** Expands the size of the period by the duration on both ends.
   *
   *So before expand 
   *@code
   *
   *         [-------]
   * ^   ^   ^   ^   ^   ^  ^
   * 1   2   3   4   5   6  7
   * 
   *@endcode
   * After expand(2)
   *@code
   *
   * [----------------------]
   * ^   ^   ^   ^   ^   ^  ^
   * 1   2   3   4   5   6  7
   * 
   *@endcode
   */
  template<class point_rep, class duration_rep>
  inline
  void period<point_rep,duration_rep>::expand(const duration_rep& d)
  {
    begin_ = begin_ - d;
    last_  = last_  + d;
  }

Jeff