[Rio-pm] Perl 5.10 e Hash::Util::FieldHash

[Solli Honorio]

Eu pesquisei o Moose no inicio do ano e gostei muito da sintaxe, mas achei
muito pesado. A instalação do módulo exige um caminhão de módulos, por isto
desisti e voltei para o bom e velho Class::*.

Solli M. Honório

2008/3/25, Lorn <lorn.br em gmail.com>:
>
> Oi Breno, baseado no seu email ( não li o artigo do PerlTips :P ) eu estou
> gostando muuuito do Moose, acho que todos deveriam testar :P é bem fácil e o
> tutorial do CPAN é simples e direto.
> Esse artigo é uma boa desculpa para estudar Moose :
> http://blog.jrock.us/articles/Myth%3A%20Moose%20is%20an%20unnecessary%20dependency.pod
>
> On Tue, Mar 25, 2008 at 1:04 PM, breno <breno em rio.pm.org> wrote:
>
> > Abaixo, artigo da PerlTips. Aos programadores de plantão, uma
> > pergunta: embora o autor comente o uso do tão falado Class::Std (do
> > Conway) e do Object::InsideOut (do Hedden), ele cita o
> > Hash::Util::FieldHash como uma ótima alternativa. Pessoalmente nunca
> > usei o Object::InsideOut, mas o Class::Std parece mais um framework de
> > OO (como o Moose - embora nunca tenha usado o Moose) do que qualquer
> > outra coisa. Mesmo sendo do Conway, tenho certo receio em relação a
> > performance por todas as coisas que rolam por debaixo dos panos, e
> > pelo fato de não ser core. Já o Hash::Util::FieldHash me pareceu uma
> > solução muito mais "Perlish", pq permite a criação de objetos
> > inside-out de forma simples, preguiçosa e sem preocupações de DESTROY
> > (contra vazamento) ou CLONE (para multithreading). E agora é core.
> >
> > Qual a percepção de vcs?
> >
> > []s
> >
> > -b
> >
> >
> > ==== Perl 5.10 and Hash::Util::FieldHash ====
> >
> >   Perl 5.10 adds the ``Hash::Util::FieldHash'' module to the list of
> > core
> >   modules. Just like all of the other core modules such as
> > ``File::Find''
> >   and ``File::Temp'' this means that ``Hash::Util::FieldHash'' will now
> > be
> >   installed as standard with Perl for all versions from 5.10.0 onward.
> >
> >
> > ==   Inside-out objects and Hash::Util::FieldHash   ==
> >
> >   Inside-out objects provide a method of strong encapsulation and
> >   compile-time error checking using Perl's object oriented features.
> > This
> >   is done by keeping a separate hash for each object attribute, and
> > using
> >   a unique identifier for the object (commonly its memory address) to
> >   access these attributes.
> >
> >   You can refresh your memory of inside-out objects at our Perl tip at
> >   <http://perltraining.com.au/tips/2006-03-31.html>.
> >
> >   Unfortunately, inside-out objects have two common disadvantages:
> >
> >   1.  Care must be taken to clean-up your attribute hashes when your
> >       object is destroyed (by going out of scope, for example). If you
> >       don't do this, you can end up leaking memory.
> >
> >   2.  Care must be taken when memory addresses are used as hash keys, as
> >       these addresses may change (potentially invalidating the object)
> >       when using a forked or threaded process.
> >
> >   When working with inside-out objects, we recommend you use a helper
> >   module like ``Class::Std'' or ``Object::InsideOut'' which can solve
> > some
> >   or all of these problems for you. However if these modules are not
> >   suitable, or if you're working with existing code that does not use
> >   them, ``Hash::Util::FieldHash'' provides a convenient and reliable way
> >   to build inside-out objects.
> >
> >   Put very simply, a hash declared as a ``fieldhash'' has the following
> >   attributes:
> >
> >   *   A reference can be used directly as a hash key.
> >
> >   *   This reference will alter itself appropriately if the process
> > forks,
> >       spawns a new thread, or otherwise causes the reference to relocate
> >       in memory.
> >
> >   *   Our hash key is considered a *weak reference*, meaning that if the
> >       only use of our reference is inside ``fieldhash'' structures, then
> >       the entire key/value pair will be garbage collected. This provides
> >       for automatic destruction of any objects that fall out of scope.
> >
> >   These properties mean that we can write inside-out objects without the
> >   headaches of finding appropriate identifiers for our objects,
> >   forking/threading issues, or garbage collection. It's also possible to
> >   enable only *some* of the above features if we want more specific
> >   behaviour (see "Further reading" below).
> >
> >   Imagine a playing card as an object: it would have a suit and a face
> >   value (rank). We can use ``Hash::Util::FieldHash'' to simplify the
> >   creation of this as an inside-out object. A minimal class may look
> > like
> >   this:
> >
> >           package PlayingCard;
> >           use strict;
> >           use warnings;
> >           use Hash::Util::FieldHash qw(fieldhash);
> >
> >           fieldhash my %suit_of;
> >           fieldhash my %rank_of;
> >
> >           sub new {
> >                   my ($class, $rank, $suit) = @_;
> >
> >                   # This strange looking line produces an
> >                   # anonymous blessed scalar.
> >
> >                   my $this = bless \do{my $anon_scalar}, $class;
> >
> >                   $suit_of{ $this } = $suit;
> >                   $rank_of{ $this } = $rank;
> >
> >                   return $this;
> >           }
> >
> >           sub get_suit {
> >                   my ($this) = @_;
> >                   return $suit_of{ $this };
> >           }
> >
> >           sub get_rank {
> >                   my ($this) = @_;
> >                   return $rank_of{ $this };
> >           }
> >
> >           1;
> >
> >   What's interesting about this example is what's missing. We don't need
> > a
> >   ``DESTROY'' method for memory management, nor a ``CLONE'' method for
> >   threading. By declaring %suit_of and %rank_of with ``fieldhash'', this
> >   work is already done for us.
> >
> >   We could use our playing card as follows:
> >
> >           #!/usr/bin/perl -w
> >           use strict;
> >           use feature qw(say);
> >           use PlayingCard;
> >
> >           my $card = PlayingCard->new('ace', 'spades');
> >           say 'My rank is ', $card->get_rank;
> >           say 'My suit is ', $suit->get_suit;
> >
> >           {
> >                   my $card2 = PlayingCard->new('king', 'diamonds');
> >                   say 'My new card rank is a ', $card->get_rank;
> >           }
> >
> >   $card2 will automatically be destroyed and its memory garbage
> > collected
> >   at the end of its block.
> >
> >
> > ==   Further reading   ==
> >
> >   To find out what other modules have been included in the core read the
> >   Perl delta for 5.10.0 at <http://search.cpan.org/perldoc?perl5100delta
> > >.
> >   To learn more about ``Hash::Util::FieldHash'' read
> >   <http://search.cpan.org/perldoc?Hash::Util::FieldHash>.
> >
> >   More information about ``Class::Std'' can be found at
> >   <http://search.cpan.org/perldoc?Class::Std>, and more information
> > about
> >   ``Object::InsideOut'' can be found at
> >   <http://search.cpan.org/perldoc?Class::InsideOut>.
> > _______________________________________________
> > Rio-pm mailing list
> > Rio-pm em pm.org
> > http://mail.pm.org/mailman/listinfo/rio-pm
> >
>
>
>
> --
> Lindolfo "Lorn" Rodrigues
> - www.slackwarezine.com.br
> - http://lornlab.org
> - http://sao-paulo.pm.org
> use Catalyst;
> _______________________________________________
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>



-- 
"o animal satisfeito dorme". - Guimarães Rosa
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