[ruby-core:99248] [Ruby master Bug#17030] Enumerable#grep{_v} should be optimized for Regexp

[scivola20@gmail.com]

Issue #17030 has been updated by scivola20 (sciv ola).


I have an idea to solve it without any compatibility problem.

[1] Introduce such a Regexp object that `===` method is same as `match?`.
[2] Introduce regexp literal option that makes the Regexp object as [1].

If the option is `'f'`, we can write as `/o/f`, and `grep(/o/f)` is faster than `grep(/o/)`.

This speed up not only `grep` but also `all?`, `any?`, `case` and so on.

Many people have written like this:

```rb
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.

----------------------------------------
Bug #17030: Enumerable#grep{_v} should be optimized for Regexp
https://bugs.ruby-lang.org/issues/17030#change-86632

* Author: marcandre (Marc-Andre Lafortune)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
Currently:

```ruby
array.select { |e| e.match?(REGEXP) }

# about 3x faster and 6x more memory efficient than
array.grep(REGEXP)
```

This is because `grep` calls `Regexp#===` which creates useless `MatchData`



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