Bug #16448: regex global variables are working differently depending on scope

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin18]
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
• Tags: core

[tdrive (Stanislav Boldaev)]

Hi, everyone.

I am trying to write a code similar to this

#!/usr/bin/env ruby

def check(f1)
  f2 = ->(match) { p match; p $~ }
  
  data = "hello test test test"
  
  data.gsub(/test/, &f1)
  data.gsub(/test/, &f2)
end

check(->(match) { p match; p $~ })

output:

"test"
nil
"test"
nil
"test"
nil
"test"
#<MatchData "test">
"test"
#<MatchData "test">
"test"
#<MatchData "test">

ruby versions:
ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin18]
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-darwin18]

Why does the global variable ($~) in f1 and f2 work differently? It's a bug or my mistake?

[mame (Yusuke Endoh)]

$~ is not a global variable, but a kind of local variable. String#gsub assigns the match data to $~ of its caller. data.gsub(/test/, &f1) assigns $~ of the scope of check. The lambda f1 reads $~ of the toplevel scope, which is not set.

You can see the behavior by the following code:

def check(f1)
  data = "foobar"

  data.gsub(/foo/, &f1) #=> #<MatchData "DUMMY">
  p $~                  #=> #<MatchData "foo">

  f2 = ->(match) { p $~ }

  data.gsub(/bar/, &f2) #=> #<MatchData "bar">
  p $~                  #=> #<MatchData "bar">
end

"DUMMY" =~ /DUMMY/
check(->(match) { p $~ })

[tdrive (Stanislav Boldaev)]

It is very unexpected.(
Thank you.

[sawa (Tsuyoshi Sawada)]

• Subject changed from regex global variables are working differently depend on scope to regex global variables are working differently depending on scope
• Description updated (diff)

[jeremyevans0 (Jeremy Evans)]

• Related to Bug #8444: Regexp vars $~ and friends are not thread local added

[jeremyevans0 (Jeremy Evans)]

• Status changed from Open to Closed