为什么Perl发出的“使用不带括号的”shift“警告不明确?

用 use diagnostics ,您会收到有用的消息:

    Warning: Use of "shift" without parentheses is ambiguous at (eval
        9)[/usr/lib/perl5/5.8/perl5db.pl:628] line 2 (#1)
    (S ambiguous) You wrote a unary operator followed by something that
    looks like a binary operator that could also have been interpreted as a
    term or unary operator.  For instance, if you know that the rand
    function has a default argument of 1.0, and you write

        rand + 5;

    you may THINK you wrote the same thing as

        rand() + 5;

    but in actual fact, you got

        rand(+5);

    So put in parentheses to say what you really mean.

担心的是你会写一些 shift .5 它将被解析为 shift(0.5) .

模棱两可并不意味着真正的模棱两可,只是在解析器确定的范围内模棱两可。 shift . 尤其是“模棱两可”,因为 . 可以开始一个术语(例如 .123 )或者操作员, 因此,它还不足以决定接下来的是shift的操作数还是shift()作为操作数的运算符(而解析器也不够聪明,无法知道:a)shift()作为 . 这不是一个学期的开始还是b) 123 不是有效的移位操作数)。