perl – 我怎样才能重新定义子程序并保留旧程序？

sub first {
    print "this is original first";
}

*original_first = \&first;

sub first {
    print "this is first redefined";
}

original_first(); # i expect this to print "this is original first"
first() # i expect this to print "this is first redefined"

我认为通过首先保存符号,我以后可以调用原始子程序(名称为original_first)并且也可以先调用,然后重新定义.但是,如果我调用original_first,我仍然会得到“这是第一次重新定义”.我需要做些什么来完成这项工作？