Bug #1749: Change in How $~ is Restored After String#sub/String#gsub with a Block
http://redmine.ruby-lang.org/issues/show/1749

Author: Run Paint Run Run
Status: Open, Priority: Normal
Category: core
ruby -v: ruby 1.9.2dev (2009-07-08 trunk 23995) [i686-linux]

I wrote the following in [ruby-core:23699], but it seems to have been missed, so I'm filing it as a ticket. There are 3 RubySpec failures relating to this issue, so it would be great to determine what's what. :-)

There's been a change between 1.8 and 1.9 in how $~ is restored after String#sub with a block. Upon leaving the #sub block, 1.8 restores $~ to what #sub set it to; 1.9 retains the value of $~ that was set inside the#sub block. The following code illustrates the issue:

 [/./, "l"].each do |pattern|
   old_md = nil
   "hello".sub(pattern) do
     old_md = $~
     "ok".match(/./)
     "x"
   end

   puts "$~ == old_md? #{$~ == old_md}"                  # A
   puts "$~.string == 'hello'? #{$~.string == 'hello'}"  # B
 end

On 1.9.2 trunk, all conditionals are false; on 1.8.7/1.8.6 they're all true.

If you replace #sub with #gsub in the above example, the conditionals are still all true on 1.8. On 1.9 the $~.string conditionals (A) are now true. The MatchData comparison (B) appears to succeed from the
#inspect output, but the objects have different #hash codes, so they don't compare for equality.

Is this change intentional, or evidence of a regression? :-)


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