[ruby-core:125122] [Ruby Feature#8948] Frozen regex

24 Mar 2026

      Issue #8948 has been updated by Eregon (Benoit Daloze).

From the discussion at the dev meeting
https://github.com/ruby/dev-meeting-log/blob/master/2026/DevMeeting-2026-01-...
...
matz: try freezing Regexp instances, but no subclasses, and revisit it to check compatibility issues.
I will adjust the PR (https://github.com/ruby/ruby/pull/14547) to do that.

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Feature #8948: Frozen regex
https://bugs.ruby-lang.org/issues/8948#change-116842

* Author: sawa (Tsuyoshi Sawada)
* Status: Assigned
* Assignee: Eregon (Benoit Daloze)
* Target version: 4.1
----------------------------------------
=begin
I see that frozen string was accepted for Ruby 2.1, and frozen array and hash are proposed in https://bugs.ruby-lang.org/issues/8909. I feel there is even more use case for a frozen regex, i.e., a regex literal that generates a regex only once. It is frequent to have a regex within a frequently repeated portion of code, and generating the same regex each time is a waste of resource. At the moment, we can have a code like:

    class Foo
      RE1 = /pattern1/
      RE2 = /pattern1/
      RE3 = /pattern1/
      def classify
        case self
        when RE1 then 1
        when RE2 then 2
        when RE3 then 3
        else 4
        end
      end
    end

but suppose we have a frozen `Regexp` literal `//f`. Then we can write like:

    class Foo
      def classify
        case self
        when /pattern1/f then 1
        when /pattern1/f then 2
        when /pattern1/f then 3
        else 4
        end
      end
    end

=end

-- 
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