Makes the set compare its elements by their identity and returns self.
This method may not be supported by all subclasses of Set.
# File lib/set.rb, line 107
def compare_by_identity
if @hash.respond_to?(:compare_by_identity)
@hash.compare_by_identity
self
else
raise NotImplementedError, "#{self.class.name}\##{__method__} is not implemented"
end
end