双正斜杠在这里是什么意思? [英] what does the double forward slash mean here?

问题描述

我是 Perl 的新手，在工作中遇到了这段代码，我搜索了一段时间但没有找到答案.任何人都可以帮助用简单的英语解释它的功能吗?谢谢.

I'm new to Perl and came across this piece of code at work, I search for a while but did not find the answer. Can anyone help to explain its function in plain english? thanks.

my $abc = delete $args{ 'abc' } // croak 'some information!';

推荐答案

从此页面:http://perldoc.perl.org/perlop.html#Logical-Defined-Or

虽然在 C 中没有直接的等价物，但 Perl 的 // 运算符与其 C 风格的 or 相关.实际上，它与|| 完全相同，只是它测试的是左侧的定义性 而不是它的真相.因此，EXPR1//EXPR2 返回EXPR1 的值，否则返回EXPR2 的值.(EXPR1 在 scalar 上下文中求值，EXPR2 在 // 本身的上下文中求值).通常，这与 defined(EXPR1) 的结果相同?EXPR1 : EXPR2(除了三元运算符形式可以用作左值，而 EXPR1//EXPR2 不能，并且 EXPR1 只会被评估一次).这对于为变量提供默认值非常有用.如果您确实想测试是否至少定义了 $a 和 $b 之一，请使用 defined($a//$b).

Although it has no direct equivalent in C, Perl's // operator is related to its C-style or. In fact, it's exactly the same as ||, except that it tests the left hand side's definedness instead of its truth. Thus, EXPR1 // EXPR2 returns the value of EXPR1 if it's defined, otherwise, the value of EXPR2 is returned. (EXPR1 is evaluated in scalar context, EXPR2 in the context of // itself). Usually, this is the same result as defined(EXPR1) ? EXPR1 : EXPR2 (except that the ternary-operator form can be used as a lvalue, while EXPR1 // EXPR2 cannot, and EXPR1 will only be evaluated once). This is very useful for providing default values for variables. If you actually want to test if at least one of $a and $b is defined, use defined($a // $b).

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