unmached capture (https://github.com/ruby/strscan/pull/72) fix https://github.com/ruby/strscan/issues/70 If there is no substring matching the group (s[3]), the behavior is different. If there is no substring matching the group, the corresponding element (s[3]) should be nil. ``` s = StringScanner.new('foobarbaz') #=> #<StringScanner 0/9 @ "fooba..."> s.scan /(foo)(bar)(BAZ)?/ #=> "foobar" s[0] #=> "foobar" s[1] #=> "foo" s[2] #=> "bar" s[3] #=> nil s.captures #=> ["foo", "bar", ""] s.captures.compact #=> ["foo", "bar", ""] ``` ``` s = StringScanner.new('foobarbaz') #=> #<StringScanner 0/9 @ "fooba..."> s.scan /(foo)(bar)(BAZ)?/ #=> "foobar" s[0] #=> "foobar" s[1] #=> "foo" s[2] #=> "bar" s[3] #=> nil s.captures #=> ["foo", "bar", nil] s.captures.compact #=> ["foo", "bar"] ``` https://docs.ruby-lang.org/ja/latest/method/MatchData/i/captures.html ``` /(foo)(bar)(BAZ)?/ =~ "foobarbaz" #=> 0 $~.to_a #=> ["foobar", "foo", "bar", nil] $~.captures #=> ["foo", "bar", nil] $~.captures.compact #=> ["foo", "bar"] ``` * StringScanner#captures is not yet documented. https://docs.ruby-lang.org/ja/latest/class/StringScanner.html https://github.com/ruby/strscan/commit/1fbfdd3c6f