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require "ftw/namespace"
# A mixin that provides singleton-ness
#
# Usage:
#
# class Foo
# extend FTW::Singleton
#
# ...
# end
#
# foo = Foo.singleton
module FTW::Singleton
# This is invoked when you include this module. It raises an exception because you should be
# using 'extend' not 'include' for this module..
def self.included(klass)
raise ArgumentError.new("In #{klass.name}, you want to use 'extend #{self.name}', not 'include ...'")
end # def included
# Create a singleton instance of whatever class this module is extended into.
#
# Example:
#
# class Foo
# extend FTW::Singleton
# def bar
# "Hello!"
# end
# end
#
# p Foo.singleton.bar # == "Hello!"
def singleton
@instance ||= self.new
return @instance
end # def self.singleton
end # module FTW::Singleton
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