Question

我有这两个模块：

package G1;

sub new {
    my $class = shift;
    my $self = {
        one => 1,
        two => 2,
        three => 3
    };
    bless $self,$class;
    return $self;
}

sub three {
    my $self = shift;
    print "G1 green is ",$self->{three};
}

1;

package G2;

our @ISA = qw(G1);
#use base qw(G1);

sub new {
    my $class = shift;
    my $self = $class->SUPER::new();
    $self->{three} = 90;
    bless $self,$class;
    return $self;
}

sub three {
    my $self = shift;
    print "G2 rox!\n";
    $self->SUPER::three();
}

1;

以及以下脚本：

use G2;

my $ob = G2->new();
$ob->three();

运行脚本时，会产生以下错误：

Can't locate object method "new" via package "G2" at G2.pm line 8.

如果我将@ISA行替换为use base，则脚本可以正常运行。我试图覆盖一些方法并在之后调用原始方法。我做错了什么？

Answer 1

因为G2.pm需要包含use G1;行。没有它，G1.pm永远不会被加载。如果你运行警告，Perl会告诉你：

$ perl -w t.pl
Can't locate package G1 for @G2::ISA at t.pl line 1.
Can't locate package G1 for @G2::SUPER::ISA at G2.pm line 8.
Can't locate package G1 for @G2::SUPER::ISA at G2.pm line 8.
Can't locate object method "new" via package "G2" at G2.pm line 8.

注意所有无法找到包G1 ... 错误。

要明确，use base 'G1'有效，因为它也有use G1。

Answer 2

G2需要了解G1，而不仅仅是名字。添加

require G1;

到G2.pm。

为什么在这个例子中直接设置@ISA不起作用？

2 个答案: