string.next 的反义词是什么? [英] What is the opposite of string.next?

问题描述

Ruby 中是否有与 String#succ 相反的方法?

Is there a method in Ruby that does the opposite String#succ?

如果你运行 succ 或 next 你会得到这个:

If you run succ or next you get this:

a = "4.4.10"
a.succ
=> "4.4.11"

我想要相反的:

a = "4.4.10"
a.previous
=> "4.4.09"

这可能吗?我很难在 Ruby 文档中找到它.也许它不存在?

Is this possible? I was having a hard time finding this in the Ruby docs. Maybe it doesn't exist?

推荐答案

prev 或类似的东西不在标准 API 中，因为 succ 和一个假设的 prev 是满射.尽管如此，实现 Ruby 字符串类 Prev/Pred/Prev!/Pred! - 与 Next/Succ 方法相反" 是您可以使用的可能版本.

prev or something similar is not in the standard API because succ and a hypoethetical prev are surjective. Despite this, "Implement Ruby String Class Prev / Pred / Prev! / Pred! - Opposite Of Next / Succ Methods" is a possible version you could use.

根本问题在于succ 是不可逆的.这意味着，一旦你应用了 succ，那么 prev 最终会产生一些歧义.

The root problem is that succ is not inversible. This means, once you applied succ, then prev would end up with some ambiguity.

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