Feature #21532: Define most of Pathname in Ruby code

• Status: Closed
• Assignee: Eregon (Benoit Daloze)
• Target version: -

[Eregon (Benoit Daloze)]

There was discussion in #17473 and before to define most of Pathname in Ruby code and not in the C extension.

I have made a PR to achieve that: https://github.com/ruby/pathname/pull/57
I would like to merge it soon to avoid conflicts.

Once upon a time, Pathname was pure-Ruby: https://github.com/ruby/ruby/blob/95bc02237635d3fe42532bfe53038257575cee75/lib/pathname.rb

This PR goes back to that, and reuses that original Ruby code, but keeps the C extension implementation of <=> and sub as those two are significantly faster.
The other Pathname methods are actually faster in Ruby than in C, because all these methods just do rb_funcall() and rb_ivar_get() and those in C code have no inline cache, but the corresponding method calls and @path have inline caches in Ruby code.
https://railsatscale.com/2023-08-29-ruby-outperforms-c/ is an explanation of that.

Therefore having Pathname defined in Ruby seems a clear win for many reasons:

• Much clearer implementation, so easier to read what the code does
• Easier to maintain
• Safer (no risk of accessing out of bounds memory or e.g. passing the wrong number of arguments to rb_funcall)
• Significantly faster, because of these inline caches (more details in https://github.com/ruby/pathname/pull/57#issue-3234862768):

Speedup (this branch / master)	ruby 3.4.2	ruby 3.4.2 + YJIT
Pathname.new(".")	1.02x	1.19x
Pathname#directory?	1.03x	1.06x
Pathname#to_s	1.85x	2.38x

• Better for JITs as they can optimize this, notably ... vs the C extension being a blackbox
• Works on JRuby (which does not support C extensions)
• Works on TruffleRuby (some Ruby C API functions that the extension uses are not supported on TruffleRuby)

[Eregon (Benoit Daloze)]

• Related to Feature #17473: Make Pathname to embedded class of Ruby added

[Eregon (Benoit Daloze)]

• Description updated (diff)

[Eregon (Benoit Daloze)]

• Description updated (diff)

[Eregon (Benoit Daloze)]

• Description updated (diff)

[akr (Akira Tanaka)]

Ok. Merge it.

[Eregon (Benoit Daloze)]

• Status changed from Open to Closed

Thanks!

[hsbt (Hiroshi SHIBATA)]

https://github.com/ruby/pathname/pull/57 is incomplete.

Some methods are incompatibility with C Version and Ruby version of Pathname broke with Windows platform.

https://github.com/ruby/ruby/pull/14303

[Eregon (Benoit Daloze)]

The CI did pass on Windows e.g. https://github.com/ruby/pathname/actions/runs/16760570256/job/47454475161
Are there extra Pathname tests in CRuby?
In any case, happy to take a look.