哈希中加号是什么意思？ [英] What does a plus sign mean in a hash?

问题描述

我有以下一段Perl代码，但我不知道它在做什么。

I have the following piece of Perl code, but I can't understand what its doing.

use constant ANIMAL => 'rabbit'; 
if ($self->{+ANIMAL}) {
    # Do something here
}

在常量 ANIMAL 之前的 + 符号是什么？

What does the + sign before the constant ANIMAL mean?

推荐答案

来自 perldoc常量 ：

如果在上下文中使用常量会遇到麻烦自动引用裸字（对于任何子例程调用都是如此）。例如，您不能说 $ hash {CONSTANT} ，因为 CONSTANT 将被解释为字符串。使用 $ hash {CONSTANT（）} 或 $ hash {+ CONSTANT} 可以防止裸词引用机制启动同样，由于 => 运算符立即在其左侧引用一个裸字，因此必须说 CONSTANT（）=>。 ‘value’（或只是用逗号代替大箭头），而不是 CONSTANT => ‘值’。

You can get into trouble if you use constants in a context which automatically quotes barewords (as is true for any subroutine call). For example, you can't say $hash{CONSTANT} because CONSTANT will be interpreted as a string. Use $hash{CONSTANT()} or $hash{+CONSTANT} to prevent the bareword quoting mechanism from kicking in. Similarly, since the => operator quotes a bareword immediately to its left, you have to say CONSTANT() => 'value' (or simply use a comma in place of the big arrow) instead of CONSTANT => 'value'.

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