NAME

       Heap::Elem - Perl extension for elements to be put in Heaps

SYNOPSIS

         use Heap::Elem::SomeInheritor;

         use Heap::SomeHeapClass;

         $elem = Heap::Elem::SomeInheritor->new( $value );
         $heap = Heap::SomeHeapClass->new;

         $heap->add($elem);

DESCRIPTION

       This is an inheritable class for Heap Elements.  It provides the interface documentation
       and some inheritable methods.  Only a child classes can be used - this class is not
       complete.

METHODS

       $elem = Heap::Elem::SomeInheritor->new( [args] );
           Creates a new Elem.

       $elem->heap( $val ); $elem->heap;
           Provides a method for use by the Heap processing routines.  If a value argument is
           provided, it will be saved.  The new saved value is always returned.  If no value
           argument is provided, the old saved value is returned.

           The Heap processing routines use this method to map an element into its internal
           structure.  This is needed to support the Heap methods that affect elements that are
           not are the top of the heap - decrease_key and delete.

           The Heap processing routines will ensure that this value is undef when this elem is
           removed from a heap, and is not undef after it is inserted into a heap.  This means
           that you can check whether an element is currently contained within a heap or not.
           (It cannot be used to determine which heap an element is contained in, if you have
           multiple heaps.  Keeping that information accurate would make the operation of merging
           two heaps into a single one take longer - it would have to traverse all of the
           elements in the merged heap to update them; for Binomial and Fibonacci heaps that
           would turn an O(1) operation into an O(n) one.)

       $elem1->cmp($elem2)
           A routine to compare two elements.  It must return a negative value if this element
           should go higher on the heap than $elem2, 0 if they are equal, or a positive value if
           this element should go lower on the heap than $elem2.  Just as with sort, the Perl
           operators <=> and cmp cause the smaller value to be returned first; similarly you can
           negate the meaning to reverse the order - causing the heap to always return the
           largest element instead of the smallest.

INHERITING

       This class can be inherited to provide an oject with the ability to be heaped.  If the
       object is implemented as a hash, and if it can deal with a key of heap, leaving it
       unchanged for use by the heap routines, then the following implementation will work.

         package myObject;

         require Exporter;

         @ISA = qw(Heap::Elem);

         sub new {
             my $self = shift;
             my $class = ref($self) || $self;

             my $self = SUPER::new($class);

             # set $self->{key} = $value;
         }

         sub cmp {
             my $self = shift;
             my $other = shift;

             $self->{key} cmp $other->{key};
         }

         # other methods for the rest of myObject's functionality

AUTHOR

       John Macdonald, jmm@perlwolf.com

COPYRIGHT

       Copyright 1998-2003, O'Reilly & Associates.

       This code is distributed under the same copyright terms as perl itself.

SEE ALSO

       Heap(3), Heap::Elem::Num(3), Heap::Elem::NumRev(3), Heap::Elem::Str(3),
       Heap::Elem::StrRev(3).