indexing
	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'."
	status: "See notice at end of class"
	names: comparable, comparison
	date: "$Date$"
	revision: "$Revision$"

deferred class interface
	COMPARABLE

feature -- Comparison

	is_equal (other: like Current): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object and identical to it?
		require -- from ANY
			other_not_void: other /= void
		ensure -- from ANY
			symmetric: Result implies other.is_equal (Current)
			consistent: standard_is_equal (other) implies Result
		ensure then
			trichotomy: Result = (not (Current < other) and not (other < Current))

	max (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 (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

	three_way_comparison (other: like Current): INTEGER
			-- If current object equal to other, 0;
			-- if smaller, -1; if greater, 1
		require
			other_exists: other /= void
		ensure
			equal_zero: (Result = 0) = is_equal (other)
			smaller_negative: (Result = - 1) = (Current < other)
			greater_positive: (Result = 1) = (Current > other)

	infix "<" (other: like Current): BOOLEAN
			-- Is current object less than other?
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then
			asymmetric: Result implies not (other < Current)

	infix "<=" (other: like Current): BOOLEAN
			-- Is current object less than or equal to other?
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then
			definition: Result = ((Current < other) or is_equal (other))

	infix ">" (other: like Current): BOOLEAN
			-- Is current object greater than other?
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then
			definition: Result = (other < Current)

	infix ">=" (other: like Current): BOOLEAN
			-- Is current object greater than or equal to other?
		require -- from PART_COMPARABLE
			other_exists: other /= void
		ensure then
			definition: Result = (other <= Current)
	
invariant

	irreflexive_comparison: not (Current < Current)
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

indexing
	library: "[
			EiffelBase: Library of reusable components for Eiffel.
	]"
	status: "[
			Copyright 1986-2001 Interactive Software Engineering (ISE).
			For ISE customers the original versions are an ISE product
			covered by the ISE Eiffel license and support agreements.
	]"
	license: "[
			EiffelBase may now be used by anyone as FREE SOFTWARE to
			develop any product, public-domain or commercial, without
			payment to ISE, under the terms of the ISE Free Eiffel Library
			License (IFELL) at http://eiffel.com/products/base/license.html.
	]"
	source: "[
			Interactive Software Engineering Inc.
			ISE Building
			360 Storke Road, Goleta, CA 93117 USA
			Telephone 805-685-1006, Fax 805-685-6869
			Electronic mail <info@eiffel.com>
			Customer support http://support.eiffel.com
	]"
	info: "[
			For latest info see award-winning pages: http://eiffel.com
	]"

end -- class COMPARABLE