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module Naught
module Conversions
def self.included(null_class)
unless class_variable_defined?(:@@included) && @@included
@@null_class = null_class
@@null_equivs = null_class::NULL_EQUIVS
@@included = true
end
super
end
def Null(object = :nothing_passed)
case object
when NullObjectTag
object
when :nothing_passed, *@@null_equivs
@@null_class.get(:caller => caller(1))
else
fail(ArgumentError.new("#{object.inspect} is not null!"))
end
end
def Maybe(object = nil)
object = yield if block_given?
case object
when NullObjectTag
object
when *@@null_equivs
@@null_class.get(:caller => caller(1))
else
object
end
end
def Just(object = nil)
object = yield if block_given?
case object
when NullObjectTag, *@@null_equivs
fail(ArgumentError.new("Null value: #{object.inspect}"))
else
object
end
end
def Actual(object = nil)
object = yield if block_given?
case object
when NullObjectTag
nil
else
object
end
end
end
end
|
