Feature #22137: Change `Symbol#to_s` to return frozen strings

• Status: Closed
• Assignee: -
• Target version: -

[byroot (Jean Boussier)]

Since Ruby 3.4 ([Feature #20350]) Symbol#to_s returns a chilled string, meaning mutating it emits a deprecation warning.

I believe it's now time to act on this deprecation, I'd like to request that on Ruby 4.1, Symbol#to_s always return a frozen string.

Several very large codebases include Shopify and GitHub have been running with Symbol.alias_method(:to_s, :name) without any compatibility issues whatsoever.

Making this change would allow to progressively get rid of an annoying pattern in performance sensitive code:

arg.is_a?(Symbol) ? arg.name : arg.to_s

[byroot (Jean Boussier)]

• Related to Feature #20350: Return chilled string from Symbol#to_s added

[headius (Charles Nutter)]

Related discussions in https://bugs.ruby-lang.org/issues/16150 where I proposed a way to request frozen strings from to_s. I've always been +1 for all immediate values that return the same string content every time to return frozen strings.

This has shown up as a problem in performance profiles of JRuby apps for decades.

[matz (Yukihiro Matsumoto)]

Accepted.

This is the planned conclusion of the chilled string deprecation introduced in 3.4 (#20350). Two release cycles of warnings, plus the field experience from large codebases running with the frozen behavior, give me enough confidence that the compatibility impact is small.

Matz.

[nobu (Nobuyoshi Nakada)]

I'd suggest to rename STR_CHILLED_LITERAL as STR_CHILLED simply.
We shouldn't introduce any more ad-hoc flags such _TO_S.

[byroot (Jean Boussier)]

• Status changed from Open to Closed

Applied in changeset git|105ee02159ceac96df019b7da7067254a072377e.

---

[ruby/stringio] Update str_chilled_p for Ruby 4.1
(https://github.com/ruby/stringio/pull/219)

Ref: https://github.com/ruby/ruby/pull/17781
[Feature #22137]

The only cause for chilled is now literals.
STR_CHILLED_SYMBOL_TO_S has been removed because Symbol#to_s always
return a frozen string.

https://github.com/ruby/stringio/commit/5915b45c40