note
	description: "[
				Objects that may be compared according to a total order relation
		
				Note: The basic operation is < (less than); others are defined
					in terms of this operation and is_equal.
	]"
	library: "Free implementation of ELKS library"
	status: "See notice at end of class."
	legal: "See notice at end of class."
	date: "$Date: 2020-04-15 18:06:04 +0000 (Wed, 15 Apr 2020) $"
	revision: "$Revision: 104046 $"

deferred class interface
	COMPARABLE

feature -- Comparison

	is_less alias "<" (other: like Current): BOOLEAN
			-- Is current object less than other?
		ensure then
			asymmetric: Result implies not (other < Current)

	is_less_equal alias "<=" alias "≤" (other: like Current): BOOLEAN
			-- Is current object less than or equal to other?
		ensure then
			definition: Result = ((Current < other) or (Current ~ other))

	is_greater alias ">" (other: like Current): BOOLEAN
			-- Is current object greater than other?
		ensure then
			definition: Result = (other < Current)

	is_greater_equal alias ">=" alias "≥" (other: like Current): BOOLEAN
			-- Is current object greater than or equal to other?
		ensure then
			definition: Result = (other <= Current)

	is_equal (other: like Current): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object and identical to it?
		ensure then
			trichotomy: Result = (not (Current < other) and not (other < Current))

	three_way_comparison alias "⋚" (other: like Current): INTEGER_32
			-- If current object equal to other, 0;
			-- if smaller, -1; if greater, 1
		require
			other_exists: other /= Void
		ensure
			equal_zero: (Result = 0) = (Current ~ other)
			smaller_negative: (Result = -1) = (Current < other)
			greater_positive: (Result = 1) = (Current > other)

	max alias "∨" (other: like Current): like Current
			-- The greater of current object and other
		require
			other_exists: other /= Void
		ensure
			current_if_not_smaller: Current >= other implies Result = Current
			other_if_smaller: Current < other implies Result = other

	min alias "∧" (other: like Current): like Current
			-- The smaller of current object and other
		require
			other_exists: other /= Void
		ensure
			current_if_not_greater: Current <= other implies Result = Current
			other_if_greater: Current > other implies Result = other
	
invariant
	irreflexive_comparison: not (Current < Current)

note
	ca_ignore: "CA057", "CA057: simplifiable boolean expression", "CA071", "CA071: self-comparison"
	copyright: "Copyright (c) 1984-2020, Eiffel Software and others"
	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
	source: "[
		Eiffel Software
		5949 Hollister Ave., Goleta, CA 93117 USA
		Telephone 805-685-1006, Fax 805-685-6869
		Website http://www.eiffel.com
		Customer support http://support.eiffel.com
	]"

end -- class COMPARABLE

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