Perl: Constants

Constantes en Perl y Moose

Ejemplo de como usar constantes en Perl usando Moose

{
    package Parent;
    use Moose;
    use namespace::autoclean;

    use constant MY_CONSTANT => 'CONSTANT';

    use constant {
        MY_CONSTANT => 'CONSTANT'
        NO_LEVEL => 0,
        MY_LEVEL => 1,
    };

    sub printMyConstant {
        my $self = shift;
        print &MY_CONSTANT;
    }


    __PACKAGE__->meta->make_immutable;
};

{
    package Child;
    use Moose;
    use namespace::autoclean;

    extends 'Parent';

    sub printMyLevel {
        my $self = shift;
        my $class = ref $self;

        print $class->MY_LEVEL;
        print &Parent::MY_CONSTANT;
    }
    __PACKAGE__->meta->make_immutable;
}

package main;

my $child = Child->new;
$child->printMyLevel;

Perl: Using Maybe attribute not die on undef

Perl: Moose, Using Maybe attribute not die on undef

Problema

Cuando definimos atributos en Moose con constraint en tiempo de ejecución podemos encontrarnos con el siguiente tipo de excepciones: "Attribute (AttributeName) does not pass the type constraint because: Validation failed for 'Str' with value undef"
Para evitarlo podemos usar "Maybe". A continuación un ejemplo:

Class to Test

package ClassWithMaybe;

use Moose;

has 'atributoSinConstraints' => ( 
                is => 'rw', 
                isa => 'Maybe[Str]', 
                default => '',
                reader => 'getAtributoSinConstraints',
                writer => 'setAtributoSinConstraints'
                ); # will NOT die on undef

has 'atributoConConstraints' => (
                is => 'rw', 
                isa => 'Str',
                reader => 'getAtributoConConstraints',
                writer => 'setAtributoConConstraints'
                ); # will die on undef (esto puede generar la exception mostrada anteriormente)
    
sub BUILD {
    my $self = shift;
    $self->setAtributoSinConstraints('') unless defined $self->getAtributoSinConstraints;
}

no Moose; __PACKAGE__->meta->make_immutable;

TEST

package ClassWithMaybeTest;

use Moose;
use Test::More;
use Test::Exception; #cpanm Test::Exception
use ClassWithMaybe;

throws_ok { ClassWithMaybe->new( atributoConConstraints => undef ) }
    qr/Validation failed for 'Str' with value undef/; # will die on undef
    
lives_ok  { ClassWithMaybe->new( atributoConConstraints => "with data" ) } 
    'atributoConConstraints with data ok';

lives_ok  { ClassWithMaybe->new( atributoSinConstraints => undef ) } 
    'atributoSinConstraints supplied as undef'; # will not die on undef

my $classWithMaybe = ClassWithMaybe->new( atributoSinConstraints => undef , atributoConConstraints => "with data");

is $classWithMaybe->getAtributoSinConstraints, '', "atributoSinConstraints is ''";

$classWithMaybe = ClassWithMaybe->new();
$classWithMaybe->setAtributoSinConstraints(undef);# will not die on undef

is $classWithMaybe->getAtributoSinConstraints, undef, "atributoSinConstraints is undef";

done_testing;

Run test

perl ClassWithMaybeTest.t
ok 1 - threw Regexp ((?^:Validation failed for 'Str' with value undef))
ok 2 - atributoConConstraints with data ok
ok 3 - atributoSinConstraints supplied as undef
ok 4 - atributoSinConstraints is ''
ok 5 - atributoSinConstraints is undef
1..5

References:

http://stackoverflow.com/questions/6457825/moose-perl-convert-undef-to-empty-string-or-0-rather-than-die