Heap::Elem - phpMan

NAME
    Heap::Elem - Base class for elements in a Heap

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. If there is exactly one arg, the Elem's value
        will be set to that value. If there is more than one arg provided,
        the Elem's value will be set to an anonymous hash initialized to the
        provided args (which must have an even number, of course).

    $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.)

    $elem->val( $val ); $elem->val;
        Provides a method to get and/or set the value of the element.

    $elem1->cmp($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 object 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 implemetation 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, john AT perlwolf.com

COPYRIGHT
    Copyright 1998-2007, 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).