perl - 为什么直接设置 @ISA 在此示例中不起作用？

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;

和以下脚本:

use G2;

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

当我运行脚本时，它会产生以下错误:

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，则脚本可以正常工作。我试图重写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。否则，G1.pm 永远不会被加载。如果您运行时出现警告，Perl 会告诉您:

$ 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.

请注意所有无法定位包 G1... 错误。

需要明确的是，use base 'G1' 可以工作，因为它也可以use G1。