[PerlChina] 关于Nested Object Destruction的一个问题

{ package Animal;

sub name {

my $either = shift;

ref $either

? $either->{Name}

: "an unnamed $either";

}

sub named {

my $class = shift;

my $name = shift;

my $self = { Name => $name, Color => $class->default_color };

bless $self, $class;

}

sub default_color { 'brown' }

sub DESTROY {

my $self = shift;

print '[', $self->name, " has died.]\n";

}

}

{ package Cow;

@ISA = qw( Animal );

}

{ package Barn;

sub new { bless [ ], shift }

sub add { push @{+shift}, shift }

sub contents { @{+shift} }

sub DESTROY {

my $self = shift;

print '[', $self->name, " is being destroyed...]\n";

for($self->contents) {

print ' ', $_->name, " goes homeless.\n";

}

}

}

my $barn = Barn->new;

$barn->add(Cow->named('Bessie'));

$barn->add(Cow->named('Gwen'));

print "Burn the barn:\n";

$barn = undef;

print "End of program.\n";

现在的程序的运行结果的是：

Burn the barn:

[Gwen has died.]

[Bessie has died.]

End of program.

当$barn = undef时，调用的是Animal的DESTROY方法。

我想要的结果是还要调用Barn的DESTROY方法(并且打印contents的内容)，即

Burn the barn:

Barn=ARRAY(0x541c) is being destroyed...

  Bessie goes homeless.

  Gwen goes homeless.

[Gwen has died.]

[Bessie has died.]

End of program.

问题出在那里阿？那位帮忙看看吧！

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