"state"

Yesterday I was reading this post by chromatic and I finally understood what state does. If you look at the perldoc for state you will see why. There is quite a dearth of examples there.

Anyway, here’s a real world example from our code base which uses state in a slightly different way from what is probably typical.

Before:

{
   # predeclare a day's duration as well
   # as the set of weekdays to save time
   my $day = DateTime::Duration->new(days => 1);
   my $weekdays = none(1..5);

   method date_due($start_date, $max_days) {
      my $ret = $start_date + DateTime::Duration->new(days => $max_days);
      while($ret->dow eq $weekdays) { $ret -= $day }
      return $ret;
   }
}

After:

method date_due($start_date, $min_days) {
   # state declares the variables the first time that date_due is run
   state $day = DateTime::Duration->new(days => 1);
   state $weekdays = none(1..5);

   my $ret = $start_date + DateTime::Duration->new(days => $min_days);
   while($ret->dow eq $weekdays) { $ret -= $day }
   return $ret;
}

I agree with chromatic on this one; it’s not lifechangingly better, but given enough usage I think it could make things much more clear.

Posted Sun, Apr 25, 2010

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