bbatsov/ruby-style-guide — pull request #368 by IronSavior (2014-09-22 19:13:11+00:00)
Title: Add acceptable use case for !!

The original sentiment is correct for most contexts. However, it is still acceptable to use `!!` when you don't necessarily want to expose the value of the expression, but you do want to expose whether or not it is nil/false.