{
    package Barn;

    sub new { bless [],shift }

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

    sub contents { @{ +shift } }

    sub DESTROY {
        my $self = shift;
        print "$self is being destroyed...\n";
        for ( $self->contents ) {
            print ' ',$_->name," goes homeless.\n";
        }
    }
}

in this I can’t understand the work of plus sign with shift
operator. In text they said,the plus sign is like bareword it would
be interpreted as a soft reference: @{“shift”}

你能清楚地解释一下使用带加号运算符的加号的工作吗？