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posted by on Sunday March 26 2017, @11:59PM   Printer-friendly
from the hooray-for-regex dept.

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


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  • (Score: 0) by Anonymous Coward on Monday March 27 2017, @09:29AM

    by Anonymous Coward on Monday March 27 2017, @09:29AM (#484559)

    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".