use fields
In the Pet
module:
package Pet; use strict; use fields qw(name weight _Pet_pid); my $PID = 0; sub new { my Pet $self = shift; unless (ref $self) { $self = fields::new($self); $self->{_Pet_pid} = "this is Pet's secret ID"; } $self->{name} = "Hey, you!"; $self->{weight} = 20; return $self; } 1;
In a separate program, demopet:
use Pet; my Pet $rock = new Pet; # typed lexical $rock->{name} = "quartz"; $rock->{weight} = "2kg"; $rock->{_Pet_pid} = 1233; # private attribute $rock->{color} = "blue"; # generates compile-time error
In the Dog
module:
package Dog; use strict; use base 'Pet'; # inherit fields and methods from Pet use fields qw(name pedigree); # override Pet name attribute, # add new pedigree attribute use fields qw(wag _Dog_private); # not shared with Pet sub new { my $class = shift; my $self = fields::new($class); $self->SUPER::new(); # init base fields $self->{pedigree} = "none"; # init own fields return $self; }
In a separate program, demodog:
use Dog;my Dog $spot = new Dog; # typed lexical $spot->{name} = "Theloneus"; # not inherited $spot->{weight} = "30lbs"; # inherited $spot->{pedigree} = "mutt"; # not inherited $spot->{color} = "brown"; # generates compile-time error $spot->{_Pet_pid} = 3324; # generates compile-time error
The fields
pragma provides a method of
declaring class fields that can be type checked at compile time. This
relies on a feature known as pseudohashes: if a typed lexical variable
(my Pet $rock
) is holding a reference (the
Pet
object) and is used ...
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