[ruby-core:51731] [ruby-trunk - Bug #7678] $_ and $~ are shared across Fibers halfway

Issue #7678 has been updated by nobu (Nobuyoshi Nakada).

Description updated

I think this is one of undefined behaviors, so it would cause no compatibility issue.
We can fix it once we decide which is more desirable, shared between fibers or separate per fibers.

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Bug #7678: $_ and $~ are shared across Fibers halfway
https://bugs.ruby-lang.org/issues/7678#change-35697

Author: nobu (Nobuyoshi Nakada)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0
ruby -v: r38748


=begin
((|$_|)) and ((|$~|)) have thread local method scope, but are shared across fibers in same thread.

  $ ./ruby -v -e '/a/ =~ "a"; p $~; Fiber.new{/b/=~"b"; p $~}.resume; p $~'
  ruby 2.0.0dev (2013-01-09 trunk 38748) [x86_64-darwin11]
  #<MatchData "a">
  #<MatchData "b">
  #<MatchData "b">

But, it is cleared at (({Fiber.start})).

  $ ./ruby -v -e '/a/ =~ "a"; p $~; Fiber.new{p $~}.resume; p $~'
  ruby 2.0.0dev (2013-01-09 trunk 38748) [x86_64-darwin11]
  #<MatchData "a">
  nil
  nil

These two behaviors seem mismatched.  I think:

* If they should be shared, then the latter example should show same
  (({MatchData})) 3 times.

* If they should be cleared at starting fibers, those variables in the
  original fiber should be unchanged.
=end



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