All MatchData objects resulting from an invocation of String#scan are updated
with the current match
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Key: JRUBY-6141
URL: https://jira.codehaus.org/browse/JRUBY-6141
Project: JRuby
Issue Type: Bug
Components: Standard Library
Affects Versions: JRuby 1.6.4
Reporter: Jeff Pace
Assignee: Thomas E Enebo
Attachments: rubyregexp.patch, test_string_scan.rb
Each iteration of String#scan should result in a unique MatchData returned by
Regexp.last_match, with each MatchData object reflecting the results of its
match. Thus if String#scan resulted in two matches, after the first match
Regexp.last_match would have different values than Regexp.last_match would have
after the second match.
However, in the current implementation each MatchData resulting from an
invocation of String#scan has the values of the most recent match. For example,
from the attached unit test:
{noformat}
def test_scan
firstmatch = nil
str = "testing"
re = Regexp.new('(t[^t]*)')
str.scan(re) do |match|
if firstmatch.nil?
firstmatch = Regexp.last_match
assert_equal "tes", firstmatch[0]
else
secondmatch = Regexp.last_match
assert_equal "ting", secondmatch[0]
# not the same object
assert firstmatch.object_id != secondmatch.object_id
# should still be the value of the first match
assert_equal "tes", firstmatch[0]
end
end
end
{noformat}
although they are different objects (per the object_id assertions) firstmatch
and secondmatch have the same results, so the assertion:
{noformat}
assert_equal "tes", firstmatch[0]
{noformat}
will fail, with firstmatch[0] equaling "ting", the results for the second
match. (Note that this test succeeds with Ruby 1.8 and 1.9.)
The reason for this behavior is that during String#scan, a MatchData is created
for each match. The MatchData object has an attribute "regs" (org.joni.Region),
which refers to where the pattern matched in the string.
The issue is that when String#scan creates MatchData objects for each pattern
match, each of the MatchData objects refer to the same Region instance.
Subsequent matches result in the Region object being updated, and each
MatchData object sharing a reference to that Region will have the same value,
as used in MatchData#to_s and MatchData#captures.
The solution is to clone the Region object for each newly-created MatchData, as
in the attached patch.
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