[ruby-core:83411] [Ruby trunk Feature#8948] Frozen regex

Issue #8948 has been updated by shyouhei (Shyouhei Urabe).


We had a discussion around this issue at yesterday's developer meeting.

Seems everyone there agreed that in long term future, regex shall be frozen.  However the status quo is that there are wild applications that do override regex methods, particularly for testing purposes.  So there needs to be some transition paths.

Freezing regex literals sounded a good starting point.  We already optimize the return value of them:

```ruby
3.times {
  p(/foo/.object_id)
}
```

The merit of freezing regex literals are:

  - Seems very safe to do.  If it hurts someone, that means that person has already been bothered by the literal being shared among evaluations.

The disadvantage of freezing regex literals are:

  - It benefits no one while it does confuse people.  Regexp class has no built-in destructive methods so freezing them does almost nothing; just prohibits method redefinitions.  Is it worth doing by deafult?

----------------------------------------
Feature #8948: Frozen regex
https://bugs.ruby-lang.org/issues/8948#change-67376

* Author: sawa (Tsuyoshi Sawada)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
----------------------------------------
=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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