这里的双斜杠是什么意思? [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.谁能用简单的英语帮助解释它的功能?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

从此页面开始:

尽管在C语言中没有直接等效项，但是Perl的//运算符与其C样式or有关.实际上，它与||完全相同，只是它测试左侧的定义而不是其真.因此，如果已定义EXPR1 // EXPR2，则返回EXPR1的值，否则，将返回EXPR2的值. (EXPR1在标量上下文中进行评估，EXPR2在//本身的上下文中进行评估).通常，这与defined(EXPR1) ? EXPR1 : EXPR2是相同的结果(除了三元运算符形式可以用作左值，而EXPR1 // EXPR2不能，并且EXPR1仅被评估一次).这对于提供变量的默认值非常有用.如果您实际上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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