Perl 中的//= 是什么? [英] What is //= in Perl?

问题描述

我找到了一些我需要的 Perl 代码示例，但其中包含我不认识的内容.

I found an example of some Perl code I needed, but it had something in it that I didn't recognise.

my $i //= '08';

我在任何地方都找不到对此的任何参考！好像是一样的:

I can't find any reference to this anywhere! It appears to be the same as:

my $i = '08';

我错过了什么吗?

推荐答案

//= 操作符是 的赋值运算符">赋值运算符'逻辑定义或' 运算符.

The //= operator is the assignment operator version of the // or 'logical defined-or' operator.

在 my 变量声明的上下文中，变量最初是未定义的，所以它是等价于赋值(最好写成 my $i= '08';).不过总的来说，

In the context of a my variable declaration, the variable is initially undefined so it is equivalent to assignment (and would be better written as my $i = '08';). In general, though,

$i //= '08';

是以下的简写:

$i = (defined $i) ? $i : '08';

它在 Perl 操作符 (perldoc perlop) 中的两个位置(简洁地在赋值操作符部分下，以及在逻辑定义或"部分中完整描述)中有记录.它是在 Perl 5.10.0 中添加的.

It is documented in the Perl operators (perldoc perlop) in two places (tersely under the assignment operators section, and in full in the section on 'logical defined-or'). It was added in Perl 5.10.0.

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