This sounds like the question of should i inherit from a base class, or should i include an instance of some other class in my class. What i mean is, if you have a calendar class, and you want calendar functionality in a basically unrelated class, such as some specialized DB class, you probably dont want to have the DB class inherit from the Calendar class, you probably want an instance of the Calendar class in the DB, which then has a well defined interface.

package MyDBClass;

use MyCalendar;

sub new {
   my $class = shift;

   ...
   my $self = ...;
   ...
   $self->{'_calendar'} = MyCalendar->new();
   ...
   return bless $self, $class;
}

sub Calendar {
   return $self->{'_calendar'};
}

...
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Then you have a calendar as a data element of your DB class, and you can do things like:

   my $db = MyDBClass->new();

   $db->Calendar()->CalendarFunction(...);
[download]

Now there are other, more sophisticated ways to deal with the calendar in the DB, but this should illustrate the point.

The moral is, if a class wants some other packages functionality, it doesnt have to be a child class, it can just use the other class.

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