What does the !! mean in this Ruby function? [duplicate]

What does the !! mean in this Ruby function? [duplicate]

References

Reference NO 1

http://stackoverflow.com/questions/1316931/what-does-classmethod-mean-in-ruby

Reference NO 2

http://stackoverflow.com/questions/9188362/what-does-mean-in-ruby-is-it-a-block-mixed-with-a-symbol

Reference NO 3

http://stackoverflow.com/questions/16301789/what-does-mean-at-the-end-of-a-ruby-method-definition

Reference NO 4

http://stackoverflow.com/questions/1961030/ruby-ampersand-colon-shortcut

Reference NO 5

http://stackoverflow.com/questions/5231919/ruby-map-method-syntax-question

Reference NO 6

http://ruby.about.com/od/advancedruby/a/deepcopy.htm

Reference NO 7

#EANF#

Reference NO 8

#EANF#