note
	description: "References to objects containing a boolean value"
	library: "Free implementation of ELKS library"
	status: "See notice at end of class."
	legal: "See notice at end of class."
	date: "$Date: 2018-11-14 14:41:36 +0000 (Wed, 14 Nov 2018) $"
	revision: "$Revision: 102457 $"

class interface
	BOOLEAN_REF

create 
	default_create

feature -- Access

	item: BOOLEAN
			-- Boolean value

	hash_code: INTEGER_32
			-- Hash code value
	
feature -- Conversion

	to_reference: BOOLEAN_REF
			-- Associated reference of Current
		ensure
			to_reference_not_void: Result /= Void
			same_item: Result.item = item

	to_integer: INTEGER_32
			-- 1 if True
			-- 0 if False
		ensure
			not_item_implies_zero: not item implies Result = 0
			item_implies_one: item implies Result = 1
	
feature -- Element change

	set_item (b: BOOLEAN)
			-- Make b the item value.
	
feature -- Basic operations

	conjuncted alias "and" (other: like Current): BOOLEAN
			-- Boolean conjunction with other
		require
			other_exists: other /= Void
		ensure
			de_morgan: Result = not (not Current or not other)
			commutative: Result = (other and Current)
			consistent_with_semi_strict: Result implies (Current and then other)

	conjuncted_semistrict alias "and then" (other: like Current): BOOLEAN
			-- Boolean semi-strict conjunction with other
		require
			other_exists: other /= Void
		ensure
			de_morgan: Result = not (not Current or else not other)

	implication alias "implies" (other: like Current): BOOLEAN
			-- Boolean implication of other
			-- (semi-strict)
		require
			other_exists: other /= Void
		ensure
			definition: Result = (not Current or else create {BOOLEAN}.make_from_reference (other))

	negated alias "not": BOOLEAN
			-- Negation

	disjuncted alias "or" (other: like Current): BOOLEAN
			-- Boolean disjunction with other
		require
			other_exists: other /= Void
		ensure
			de_morgan: Result = not (not Current and not other)
			commutative: Result = (other or Current)
			consistent_with_semi_strict: Result implies (Current or else other)

	disjuncted_semistrict alias "or else" (other: like Current): BOOLEAN
			-- Boolean semi-strict disjunction with other
		require
			other_exists: other /= Void
		ensure
			de_morgan: Result = not (not Current and then not other)

	disjuncted_exclusive alias "xor" (other: like Current): BOOLEAN
			-- Boolean exclusive or with other
		require
			other_exists: other /= Void
		ensure
			definition: Result = ((Current or other) and not (Current and other))
	
feature -- Output

	out: STRING_8
			-- Printable representation of boolean
	
invariant
	involutive_negation: (not (not Current)).item = item
	non_contradiction: not ((not Current) and create {BOOLEAN}.make_from_reference (Current))
	completeness: (not Current) or create {BOOLEAN}.make_from_reference (Current)

note
	ca_ignore: "CA015", "CA015: double negation"
	copyright: "Copyright (c) 1984-2018, 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 BOOLEAN_REF

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