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Ruby 2.4.1 was released this week and included an upgrade to its underlying regular expression engine, Onigmo. The headline feature in this update was support for 'the absent operator' but what is this and what is it for?
An issue on the Onigmo repository about the absent operator pointed to a Japanese academic paper [PDF] that, to my delight, uses Ruby for its examples. Not being a reader of Japanese, I struggled to grasp the concept but it seemed to promise to provide developers with a new mechanism to more easily notate complex matches.
The next step towards an absent operator in Ruby's regular expressions system dates back 5 years to a suggestion for adding a 'negation flag'. It was suggested that a v flag could negate a regular expression. For example, /(?v:ruby)/ would match anything that /ruby/ didn't.
Source: https://medium.com/rubyinside/the-new-absent-operator-in-ruby-s-regular-expressions-7c3ef6cd0b99
(Score: 1) by tftp on Monday March 27 2017, @02:31AM (10 children)
I don't know Ruby or Japanese, but in Perl
For example, /(?v:ruby)/ would match anything that /ruby/ didn't.
the same thing would roughly be:
if ($_ =~ m|^(.*)ruby(.*)$|) { $_ = $1 . $2; }
(Score: 2) by Whoever on Monday March 27 2017, @02:34AM (1 child)
Only if there was only one instance of "ruby" in the string.
(Score: 1, Funny) by Anonymous Coward on Monday March 27 2017, @02:36AM
Ah, I see - you want the whole CPAN module right now :-)
(Score: 2) by jcross on Monday March 27 2017, @03:26AM
Ah, ruby and perl, the scrapple of computer languages.
(Score: 0) by Anonymous Coward on Monday March 27 2017, @03:56AM
Shouldn't read perl code on a full stomach. Ulp.
(Score: 3, Interesting) by Whoever on Monday March 27 2017, @04:24AM (1 child)
How about this to version which achieves the same objective, but also allows for multiple instances of "ruby":
s/ruby//g;
(Score: 4, Informative) by FatPhil on Monday March 27 2017, @01:06PM
If it's similar to the issue that perl went through ages back (yay - lets reinvent the wheel!), then the context may well be this: You're seaerching for "ruby up rails", "ruby in rails", "ruby by rails", "ruby plop rails", and everything that's "ruby [something] rails" but isn't "ruby on rails", then you need the "on" to be absent. Simple negations of matches in traditional regexps, such as /ruby [^o][^n] rails/, will never work. Things that would work tend to have unpleasant explosion of complexity: /ruby (.|o[^n]|[^o]n|...+) rails/, which isn't even correct despite superficially being so - more explosion is required, and don't generalise easily to anything apart from single fixed strings.
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 1) by Mike on Monday March 27 2017, @04:46AM (1 child)
I may not be understanding the issue, but it would likely be simpler in Perl to just do
( !~ /ruby/ )
Not sure why Ruby wouldn't have something like this, but I haven't played with Ruby.
(Score: 0) by Anonymous Coward on Monday March 27 2017, @09:29AM
Well, the article goes into depth why it is not a negation operator. For example, if you don't require a full-string match, matching on "(absent ruby) on rails" does give you a match for "ruby on rails", as e.g. "uby on rails" is a substring that starts with something not matching "ruby" and continues with " on rails".
(Score: 3, Informative) by bzipitidoo on Monday March 27 2017, @05:47AM (1 child)
How about:
grep -v ruby
(Score: 2) by pkrasimirov on Tuesday March 28 2017, @08:32AM
That's exactly what they did, up to the 'v'.