/usr/bin/perl
use strict;
use Scalar::Util qw/weaken isweak/;
my $foo = {};

my $bar = returnweak();
print "returnweak isweak - ".(isweak($bar)? "yes":"no")." - '$bar'\n";

weakenbyref(\$bar);
print "weakenbyref isweak - ".(isweak($bar)? "yes":"no")." - '$bar'\n";

sub returnweak {
        my $ret = $foo;
        weaken($ret);
        return $ret;
}

sub weakenbyref {
        my $arg = shift;
        weaken($$arg = $foo);
        return;
}