[ruby-core:124137] [Ruby Feature#8948] Frozen regex

11 Dec 2025

      Issue #8948 has been updated by mame (Yusuke Endoh).

Here is the code we found in the dev meeting:

https://github.com/ctrochalakis/mongo-ruby-driver/blob/e632eb570d2f42bddc670...

```ruby
  class LazyRegexp < Regexp
...

    def initialize(source, **options)
      @lazy_source = source
      super(source.to_s, **options)
    end
```

https://github.com/wallaby-rails/wallaby-rails/blob/e1d2e748887bbbdf024eb246...

```ruby
  class RegexpOfHolding < Regexp
...
    def initialize(str, options, extra_options_str)
...
      super(str, options)
      @extra_options_str = extra_options_str
    end
  end
```

Also, your PR changes the behavior of `Marshal.load` for a Regexp with encoding:

```diff
-    assert_equal(/u/, Marshal.load("\004\bI/\a\\u\000\006:\016@encoding\"\vEUC-JP"))
+    assert_raise(FrozenError) { Marshal.load("\004\bI/\a\\u\000\006:\016@encoding\"\vEUC-JP") }
```

This incompatibility should be fixed. Also, as a general rule, please clearly state when a PR includes such known incompatibilities.

----------------------------------------
Feature #8948: Frozen regex
https://bugs.ruby-lang.org/issues/8948#change-115593

* Author: sawa (Tsuyoshi Sawada)
* Status: Assigned
* Assignee: Eregon (Benoit Daloze)
----------------------------------------
=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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