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Re: Efficient Linked Lists

by pg (Canon)
on Feb 01, 2003 at 07:09 UTC ( #231810=note: print w/ replies, xml ) Need Help??


in reply to Efficient Linked Lists

Linked list is doable in Perl, and in general, linked list has its own benefits under certain context. You are not the first person talking about this, and you are not alone. I read about this topic a while ago, in couple of published Perl books.

Here is a quick OO solution I put together. It is only to prove the concept, and it obviously does not implement all the needed methods. The test case I given below worked, but there is no other test case being tried.

The solution is OO. In DoubleLinkedList.pm, the process_thru_forward and process_thru_backward functions allow you to specify callback functions and parameters to callback functions, and they are very flexible.

DoubleLinkedListElement.pm: package DoubleLinkedListElement; use Hash::Util (lock_keys); use strict; sub new { my $self = {}; $self->{VALUE} = undef; $self->{NEXT} = undef; $self->{PREV} = undef; bless $self; lock_keys(%$self); return $self; } sub value { my $self = shift; if (@_) { $self->{VALUE} = shift; } return $self->{VALUE}; } sub next { my $self = shift; my $ret = $self->{NEXT}; if (@_) { $self->{NEXT} = shift; } return $ret; } sub prev { my $self = shift; my $ret = $self->{PREV}; if (@_) { $self->{PREV} = shift; } return $ret; } 1; DoubleLinkedList.pm: package DoubleLinkedList; use DoubleLinkedListElement; use Hash::Util (lock_keys); use strict; sub new { my $self = {}; $self->{FIRST} = undef; $self->{LAST} = undef; bless $self; lock_keys(%$self); return $self; } sub first { my $self = shift; return $self->{FIRST}; } sub last { my $self = shift; return $self->{LAST}; } sub append { my ($self, $value) = @_; my $element = new DoubleLinkedListElement(); $element->value($value); if ($self->last()) { $self->last()->next($element); $element->prev($self->last()); $self->{LAST} = $element; } else { $self->{FIRST} = $element; $self->{LAST} = $element; } } sub process_thru_forward { my ($self, $func, @param) = @_; for (my $this = $self->first(); $this; $this = $this->next()) { &$func($this, @param); } } sub process_thru_backward { my ($self, $func, @param) = @_; for (my $this = $self->last(); $this; $this = $this->prev()) { &$func($this, @param); } } 1; test.pl: use Data::Dumper; use DoubleLinkedList; use strict; my $dl_list = new DoubleLinkedList; foreach (1..10) { $dl_list->append($_); } $dl_list->process_thru_forward(\&plus_and_display, 10); $dl_list->process_thru_backward(\&plus_and_display, 10); sub plus_and_display { my ($this, $adj) = @_; print $this->value + $adj, "\n"; }


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