|| =(等于)在Ruby中是什么意思? [英] What does ||= (or-equals) mean in Ruby?

问题描述

以下代码在Ruby中意味着什么?

What does the following code mean in Ruby?

||=

语法是否有任何含义或原因?

Does it have any meaning or reason for the syntax?

推荐答案

这个问题在Ruby邮件列表和Ruby博客上讨论得如此频繁，以至于Ruby邮件列表上甚至还有一些线程，其唯一目的是为了收集讨论该问题的Ruby邮件列表上的所有其他线程的链接.

This question has been discussed so often on the Ruby mailing-lists and Ruby blogs that there are now even threads on the Ruby mailing-list whose only purpose is to collect links to all the other threads on the Ruby mailing-list that discuss this issue.

这里是一个:确定的|| =(或等于)线程和页面列表

如果您真的想知道发生了什么，请查看

If you really want to know what is going on, take a look at Section 11.4.2.3 "Abbreviated assignments" of the Ruby Language Draft Specification.

作为第一近似值

a ||= b

等效于

a || a = b

和不等同于

a = a || b

但是，这仅仅是一个近似值，尤其是在未定义a的情况下.语义还取决于是简单变量分配，方法分配还是索引分配:

However, that is only a first approximation, especially if a is undefined. The semantics also differ depending on whether it is a simple variable assignment, a method assignment or an indexing assignment:

a    ||= b
a.c  ||= b
a[c] ||= b

所有待遇都不同.

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