In what circumstances are instance variables declared as '_var' in 'use fields' readonly?
- by Pedro Silva
I'm trying to understand the behavior of the fields pragma, which I find poorly documented, regarding fields prefixed with underscores. This is what the documentation has to say about it:
Field names that start with an underscore character are made private to the class and are not visible to subclasses. Inherited fields can be overridden but will generate a warning if used together with the -w switch.
This is not consistent with its actual behavior, according to my test, below. Not only are _-prefixed fields visible within a subclass, they are visible within foreign classes as well (unless I don't get what 'visible' means). Also, directly accessing the restricted hash works fine.
Where can I find more about the behavior of the fields pragma, short of going at the source code?
{
package Foo;
use strict;
use warnings;
use fields qw/a _b __c/;
sub new {
my ( $class ) = @_;
my Foo $self = fields::new($class);
$self->a = 1; $self->b = 2; $self->c = 3;
return $self;
}
sub a : lvalue { shift->{a} }
sub b : lvalue { shift->{_b} }
sub c : lvalue { shift->{__c} }
}
{
package Bar;
use base 'Foo';
use strict;
use warnings;
use Data::Dumper;
my $o = Bar->new;
print Dumper $o; ##$VAR1 = bless({'_b' => 2, '__c' => 3, 'a' => 1}, 'Foo');
$o->a = 4; $o->b = 5; $o->c = 6;
print Dumper $o; ##$VAR1 = bless({'_b' => 5, '__c' => 6, 'a' => 4}, 'Foo');
$o->{a} = 7; $o->{_b} = 8; $o->{__c} = 9;
print Dumper $o; ##$VAR1 = bless({'_b' => 8, '__c' => 9, 'a' => 7}, 'Foo');
}
