perl - "evaluated directly for a Boolean result, and no smartmatching occurs"中的 "Programming Perl"是什么意思？

Question

在“Programming Perl”一书中有一个片段(剪切):

By default, when(EXPR) is treated as an implicit smartmatch of $_; that is, $_ ~~ EXPR. However, if the EXPR argument to when is one of the 10 exceptional forms listed below, it is evaluated directly for a Boolean result, and no smartmatching occurs:

1. ...

2. A regular expression match in the form of /REGEX/, $foo =~ /REGEX/, or $foo =~ EXPR.

什么意思 evaluated directly for a Boolean result ?

例子:

#!/usr/bin/perl
use v5.14;
my @a = ('aaa', 'bbb', 'ccc');

given(@a) {
    when (/a/) { say '@a contains an a'; }
    default    { say '@a does not contain an a' }
}

当我运行它时，输出会不时变化:

@a does not contain an a

@a contains an a

@a does not contain an a

@a does not contain an a

我不明白这里发生了什么，有人能乐于助人吗？

提前欣赏。

Answer 1

仔细阅读文档:

Another useful shortcut is that, if you use a literal array or hash as the argument to "given", it is turned into a reference. So "given(@foo)" is the same as "given(\@foo)", for example.

因此， given (@a)变成了 given(\@a) .没有智能匹配，因为你用的是 when (/a/) ，所以你试图匹配

\@a =~ /a/

引用是字符串化的。它有时包含“a”，如 ARRAY(0x9a4e7f8) ，但通常不会:-)