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.

根据我的测试,这与其实际行为不一致.不仅_-前缀字段在子类中可见,它们在外部类中也是可见的(除非我没有得到“可见”的含义).此外,直接访问受限制的哈希工作正常.

在哪里可以找到更多关于字段pragma的行为,而不是源代码？

{
    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');
}