ruby - nil.to_s 产生一个卡住的字符串？

Question

我很好奇。下面的代码片段产生 FrozenError 是否令人惊讶？ ?神奇评论# frozen_string_literal: true不存在。

n = nil
s = n.to_s
s.force_encoding('UTF-8')

Answer 1

这是在 Ruby 2.7 中添加的——它明确记录在 release notes 中。 .

Module#name, true.to_s, false.to_s, and nil.to_s now always return a frozen String. The returned String is always the same for a given object. [Experimental] [Feature #16150]

链接的问题在更改背后有其他原因:

Much of the time when a user calls to_s, they are just looking for a simple string representation to display or to interpolate into another string. In my brief exploration, the result of to_s is rarely mutated directly.

It seems that we could save a lot of objects by providing a way to explicitly request a frozen string....This would reduce string allocations dramatically when applied to many common to_s calls.

总之，它减少了对象分配，从而减少了垃圾收集开销，从而提高了性能。