Feature #16294: Make MatchData frozen and forbid MatchData.allocate

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

[Eregon (Benoit Daloze)]

Currently, MatchData.allocate is allowed, but almost every MatchData method called on it raise TypeError, 'uninitialized Match'.

I think MatchData should be frozen, none of its internal fields are mutable and I don't see any use case for storing instance variables on it.
Once frozen, we can implement MatchData#dup and #clone as just return self, and we don't need to check for the uninitialized case.
And Marshal can have special treatment to create an initialized MatchData directly.

My main motivation is looking at the code in TruffleRuby required to implement MatchData.allocate and check if it's initialized in so many places:
https://github.com/oracle/truffleruby/pull/1792/files

Thoughts? Anyone against?
cc @alanwu (Alan Wu)

[nobu (Nobuyoshi Nakada)]

• Subject changed from Make MatchData frozen and forbid MatchData#allocate to Make MatchData frozen and forbid MatchData.allocate

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset git|aa94245a09887f95bc0cd353b3462108d76d13ed.

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Undefine MatchData.allocate [Feature #16294]

[nobu (Nobuyoshi Nakada)]

It would be OK to remove MatchData.allocate, I think.
And Regexp.allocate too, but rubyspec has a couple of code using Regexp.allocate.

[mame (Yusuke Endoh)]

I'm not against the proposal itself, but is it okay to introduce an incompatibility at this time? cc: @naruse (Yui NARUSE)

[Eregon (Benoit Daloze)]

@nobu (Nobuyoshi Nakada) Thanks for the change! I'll adapt the specs.

[nobu (Nobuyoshi Nakada)]

I've forgot this for years, and just happened to discover this branch.
https://github.com/ruby/ruby/pull/8624

[Eregon (Benoit Daloze)]

Looks good, I think we should merge it.
(and this is already the case on TruffleRuby)

[nobu (Nobuyoshi Nakada)]

At the latest dev-meeting, there was a suggestion that whereas MatchData cannot be dumped, Regexp.allocate might be used by serializer libraries.

[Eregon (Benoit Daloze)]

nobu (Nobuyoshi Nakada) wrote in #note-8:

At the latest dev-meeting, there was a suggestion that whereas MatchData cannot be dumped, Regexp.allocate might be used by serializer libraries.

That does not seem used in practice.
TruffleRuby already does not define Regexp.allocate, and there seems to be no compatibility issue with that except some ruby/spec specs.
Regexp.new (or eval) is good enough for deserializing regexps.