From: eregontp@... Date: 2020-10-24T14:30:06+00:00 Subject: [ruby-core:100523] [Ruby master Feature#17206] Introduce new Regexp option to avoid global MatchData allocations Issue #17206 has been updated by Eregon (Benoit Daloze). scivola20 (sciv ola) wrote in #note-5: > I believe that people who can use `match?` and `match` methods properly, can use this new Regexp option properly. I disagree, `match?` is clear, I think `=~` suddenly not setting `$~` would be a frequent source of bugs. > By the way, the total size of ``$` ``, `$&`, `$'` equals to the size of the target string. Therefore a huge amount of String garbage will be generated, if the text is very large. They are all based on `$~`, isn't it? I think they only need a copy-on-write copy of the source string (to avoid later mutations affecting them) + the matched offsets. At least that's what happens in TruffleRuby. ---------------------------------------- Feature #17206: Introduce new Regexp option to avoid global MatchData allocations https://bugs.ruby-lang.org/issues/17206#change-88145 * Author: fatkodima (Dima Fatko) * Status: Open * Priority: Normal ---------------------------------------- Originates from https://bugs.ruby-lang.org/issues/17030 When this option is specified, ruby will not create global `MatchData` objects, when not explicitly needed by the method. If the new option is named `f`, we can write as `/o/f`, and `grep(/o/f)` is faster than `grep(/o/)`. This speeds up not only `grep`, but also `all?`, `any?`, `case` and so on. Many people have written code like this: ```ruby IO.foreach("foo.txt") do |line| case line when /^#/ # do nothing when /^(\d+)/ # using $1 when /xxx/ # using $& when /yyy/ # not using $& else # ... end end ``` This is slow, because of the above mentioned problem. Replacing `/^#/` with `/^#/f`, and `/yyy/` with `/yyy/f` will make it faster. Some benchmarks - https://bugs.ruby-lang.org/issues/17030#note-9 which show `2.5x` to `5x` speedup. PR: https://github.com/ruby/ruby/pull/3455 -- https://bugs.ruby-lang.org/ Unsubscribe: