[ruby-core:93091] [Ruby trunk Feature#15836] [Proposal] Make Module#name and Symbol#to_s return their internal fstrings

[matz@ruby.or.jp]

Issue #15836 has been updated by matz (Yukihiro Matsumoto).

Status changed from Feedback to Rejected

The compatibility breakage from changing those methods (especially `Symbol#to_s`) is too big. Sorry.
Maybe we should work on `HashWithIndifferentAccess` to improve (memory) performance.

Matz.

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Feature #15836: [Proposal] Make Module#name and Symbol#to_s return their internal fstrings
https://bugs.ruby-lang.org/issues/15836#change-78513

* Author: byroot (Jean Boussier)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
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# Why ?

In many codebases, especially Rails apps, these two methods are the source of quite a lot of object allocations.

`Module#name` is often accessed for various introspection features, autoloading etc.

`Symbol#to_s` is access a lot by HashWithIndifferentAccess other various APIs accepting both symbols and strings. 

Returning fstrings for both of these methods could significantly reduce allocations, as well as sligthly reduce retention as it would reduce some duplications.

Also, more and more Ruby APIs are now returning fstrings. `frozen_string_literal`AFAIK should become the default some day, string used as hash keys are now automatically interned as well.

### Backward compatibilty 

Of course this is not fully backward compatible, it's inevitable that some code in the wild is mutating the strings returned by these methods, but I do believe it's a rare occurence, and easy to fix. 

### Implementation

I implemented it here: https://github.com/ruby/ruby/pull/2175



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