In either case, when an assertion fails, it prints the file name, line number, and a message that you can customize. 当断言失败时,这两者都输出文件名、行号和可定制的消息。
To handle this case correctly, the following if statement would explicitly set lastline to the line number of the end of file ( that is, to the line number returned by line ( ' $ ' )). 要正确地处理这种情况,随后的if语句需要显式地将lastline设置为文件末端的行号(即设置为由line('$')返回的行号)。