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Moose (Perl 5)

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These are the slides from a lecture I did on Moose, the post-modern metaclass-based object system for Perl 5.

These are the slides from a lecture I did on Moose, the post-modern metaclass-based object system for Perl 5.

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Transcript

  • 1. Moose A postmodern metaclass-based object system for Perl 5
  • 2. Objects in Perl 5 (a short intro)
    • A blessed hashref
    • 3. Manual new() method
    • 4. No real attributes
    bless {}, __PACKAGE__; sub new { my ( $class, @args ) = @_; my $self = { @args }; # params bless $self, $class; return $self; } sub name { my ( $self, $name ) = @_; $name and $self->{'name'} = $name; return $self->{'name'}; }
  • 5. Why would you want to use Moose? Moose package Person; use strict; use warnings; use Carp qw( confess ); use DateTime; use DateTime::Format::Natural; sub new { my $class = shift; my %p = ref $_[0] ? %{ $_[0] } : @_; exists $p{name} or confess 'name is a required attribute'; $class->_validate_name( $p{name} ); exists $p{birth_date} or confess 'birth_date is a required attribute'; $p{birth_date} = $class->_coerce_birth_date( $p{birth_date} ); $class->_validate_birth_date( $p{birth_date} ); $p{shirt_size} = 'l' unless exists $p{shirt_size}: $class->_validate_shirt_size( $p{shirt_size} ); return bless p, $class; } sub _validate_name { shift; my $name = shift; local $Carp::CarpLevel = $Carp::CarpLevel + 1; defined $name or confess 'name must be a string'; } Plain old Perl 5 package User; use Email::Valid; use Moose; use Moose::Util::TypeConstraints; extends 'Person'; subtype 'Email' => as 'Str' => where { Email::Valid->address($_) } => message { "$_ is not a valid email address" }; has email_address => ( is => 'rw', isa => 'Email', required => 1, );
  • 6. Get it?
  • 7. Defining an object in Moose package User; use Moose; 1; You get:
  • 12. Full-Affordance accessors
    • ' ro ' is also available for read-only attributes!
    • 13. You can set the getter or setter manually via reader / writer
    • 14. I'll show more attribute options later on
    has name => ( is => 'rw', );
  • 15. An attribute with type constraint
    • Lots of types: Str , Int , ArrayRef , HashRef , CodeRef , Regexp
    • 16. You can combine: ArrayRef[Str] , HashRef[ArrayRef[Int]]
    • 17. They have inheritance: Int is a Num
    • 18. Roll your own using subtype
    package User; use Moose; has name => ( is => 'rw', isa => 'Str', ); 1;
  • 19. Methods are the same as before sub method { my $self = shift; ... $self->more(); }
  • 20. Inheritance is as easy as...
    • Multiple inheritance is also possible, extends accepts an array
    package Punk; use Moose; extends 'Person'; 1; package Child; use Moose; extends qw/ Father Mother /; 1;
  • 21. Roles are even easier!
    • Multiple roles are recommend! with accepts an array too
    package Punk; use Moose; extends 'Person'; with 'Piercings'; 1; package Punk; use Moose; extends 'Person'; with qw/ Piercings Tattoos /; 1;
  • 22. More hooks than a coat rack! package User::Secure; use Moose; extends 'User'; before login => sub { my $self = shift; $self->security_check(); }; 1;
  • 27. Back to attributes options... has set => ( is => 'rw', isa => 'Set::Object', default => sub { Set::Object->new }, required => 1, lazy => 1, predicate => 'has_set', clearer => 'clear_set', builder => 'build_set', );
  • 28. Attribute options default => 'kitteh', # string default => 3, # number default => sub { {} }, # HashRef default => sub { [] }, # ArrayRef default => sub { Object->new }, # an Object etc. etc. (if you need a more elaborate sub, use builder ) default
  • 29. Attribute options required => 1, # required required => 0, # not required required
  • 30. Attribute options lazy => 1, # make it lazy Class will not create the slot for this attribute unless it absolutely has to. That is defined by whether it is accessed at all. Wasn't accessed? You don't pay the penalty! :) lazy = good lazy
  • 31. Attribute options builder => 'build_it', # subroutine name sub build_it { my $self = shift; # not a problem! return Some::Object->new( $self->more_opts, ); } # and, obviously... after build_it => sub { “they will come” }; (a builder sets the value of the attribute) builder
  • 32. Attribute options clearer => 'clear_it', # subroutine name # you don't need to create the subroutine sub time_machine { my $self = shift; $self->clear_it; # 'it' never happened :) } (a clearer clears the attribute, not just the value) clearer
  • 33. Attribute options predicate => 'has_it', # subroutine name # you don't need to create the subroutine sub try_to_do_it { my $self = shift; $self->has_it && $self->do_it(); } (a predicate checks an attribute exists) (even false values) (which is good!) predicate
  • 34. Attribute options lazy_build => 1, # <3 # the same as: lazy => 1, builder => '_build_it', # private clearer => 'clear_it', predicate => 'has_it', ( lazy_build is recommended) lazy_build
  • 35. Moose