From: Suraj Kurapati <sunaku@...>
Date: 2011-11-09T08:32:25+09:00
Subject: [ruby-core:40861] [ruby-trunk - Feature #5588] add negation flag (v) to Regexp


Issue #5588 has been updated by Suraj Kurapati.


I tried to implement this feature in this patch:
https://github.com/sunaku/ruby/commit/79305ba55c7ece5501c9219942eaf30e01a370a9

I was able to make Ruby recognize 'v' as an embedded regexp flag,
and was able to create regexps via the new Regexp::NEGATED constant.

However, I am stuck on the following things.  Any tips? :-)

* We can pass '(?v:)' in embedded regexp but it does not take effect.
  The resulting regexp object's #options field does not reflect 'v'.

* Make the parser accept 'v' as option at the end of literal regexps.

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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