From: Suraj Kurapati <sunaku@...>
Date: 2011-11-14T06:27:03+09:00
Subject: [ruby-core:40994] [ruby-trunk - Feature #5588] add negation flag (v) to Regexp


Issue #5588 has been updated by Suraj Kurapati.


I beautified my patches so they are easier to understand (especially the additions to test_regexp.rb in Ruby's test suite) and extracted the Oniguruma-only portions into a separate patch so that you can see what changes affect Ruby vs. Oniguruma.  Here are the patches:

* Negated regexps in Oniguruma 5.9.2 (already submitted to Kosako):
https://github.com/sunaku/onig-5.9.2/compare/v5.9.2...master

* Negated regexps in Oniguruma 5.9.2 plus integration in Ruby trunk:
https://github.com/sunaku/ruby/compare/5588_regexp_v

I would like your feedback on these.  Thanks for your consideration.
----------------------------------------
Feature #5588: add negation flag (v) to Regexp
http://redmine.ruby-lang.org/issues/5588

Author: Suraj Kurapati
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 


Please add a negation flag (v) to regexps which inverts them:

  "ruby" =~ /perl/v       #=> true   (turn on negation)
  "ruby" !~ /perl/v       #=> false  (turn on negation)
  "ruby" =~ /(?v:perl)/   #=> true   (turn on negation)
  "ruby" !~ /(?v:perl)/   #=> false  (turn on negation)
  "ruby" =~ /(?-v:perl)/  #=> false  (turn off negation)
  "ruby" !~ /(?-v:perl)/  #=> true   (turn off negation)

The flag name "v" comes from the ex(1) command of the same name.

This has beneficial applications where it is sometimes difficult
to construct what you want to match but much easier to construct
what you *do not* want to match.  Having this negation built in
the regexp itself would remove the need for us to change our 
Ruby code to process a regexp in a different way.  

For example, suppose that you are passing a regexp to the `--name`
command-line option of MiniTest.  This regexp tells MiniTest to
only run those tests whose names match.  If Ruby had a negation
flag on its regexps, then it would be suddenly trivial to make
MiniTest skip certain tests by negating the regexp we pass in.

In this manner, we get a beneficial feature without ever changing
our Ruby code (the codebase of MiniTest in this example).  :-)

Thanks for your consideration.


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