note
	description: "Durations of date"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	date: "$Date: 2017-03-29 12:26:46 +0000 (Wed, 29 Mar 2017) $"
	revision: "$Revision: 100065 $"
	access: date

class 
	DATE_DURATION

create 
	make,
	make_by_days

feature -- Initialization

	make (y, m, d: INTEGER_32)
			-- Set year, month and day to y, m and d respectively.
		do
			year := y
			month := m
			day := d
		ensure
			year_set: year = y
			month_set: month = m
			day_set: day = d
		end

	make_by_days (d: INTEGER_32)
			-- Set day to d.
			-- The duration is definite
		do
			year := 0
			month := 0
			day := d
		ensure
			day_set: day = d
			definite_duration: definite
		end
	
feature {NONE} -- Initialization

	default_create
			-- Process instances of classes with no creation clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end
	
feature -- Access

	date_default_format_string: STRING_8
			-- Default output format for dates
			-- (from DATE_CONSTANTS)
		do
			Result := Date_time_tools.Date_default_format_string
		end

	Date_time_tools: DATE_TIME_TOOLS
			-- Tools for outputting dates and times in different formats
			-- (from TIME_UTILITY)
		once
			create Result
		end

	days_in_i_th_month (i, y: INTEGER_32): INTEGER_32
			-- Number of days in the i th month at year y
			-- (from DATE_CONSTANTS)
		require -- from DATE_CONSTANTS
			i_large_enough: i >= 1
			i_small_enough: i <= Months_in_year
		do
			Result := Days_in_months @ i
			if i = 2 and then is_leap_year (y) then
				Result := Result + 1
			end
		end

	Days_in_leap_year: INTEGER_32 = 366
			-- Number of days in a leap year
			-- (from DATE_CONSTANTS)

	Days_in_non_leap_year: INTEGER_32 = 365
			-- Number of days in a non-leap year
			-- (from DATE_CONSTANTS)

	Days_in_week: INTEGER_32 = 7
			-- Number of days in a week
			-- (from DATE_CONSTANTS)

	days_text: ARRAY [STRING_8]
			-- Short text representation of days
			-- (from DATE_CONSTANTS)
		do
			Result := Date_time_tools.Days_text
		end

	default_format_string: STRING_8
			-- Default output format string
			-- (from TIME_UTILITY)
		do
			Result := Date_time_tools.Default_format_string
		end

	generating_type: TYPE [detachable DATE_DURATION]
			-- Type of current object
			-- (type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generating_type_not_void: Result /= Void
		end

	generator: STRING_8
			-- Name of current object's generating class
			-- (base class of the type of which it is a direct instance)
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			generator_not_void: Result /= Void
			generator_not_empty: not Result.is_empty
		end

	long_days_text: ARRAY [STRING_8]
			-- Long text representation of days
			-- (from DATE_CONSTANTS)
		do
			Result := Date_time_tools.Long_days_text
		end

	long_months_text: ARRAY [STRING_8]
			-- Long text representation of months
			-- (from DATE_CONSTANTS)
		do
			Result := Date_time_tools.Long_months_text
		end

	Max_weeks_in_year: INTEGER_32 = 53
			-- Maximun number of weeks in a year
			-- (from DATE_CONSTANTS)

	Months_in_year: INTEGER_32 = 12
			-- Number of months in year
			-- (from DATE_CONSTANTS)

	months_text: ARRAY [STRING_8]
			-- Short text representation of months
			-- (from DATE_CONSTANTS)
		do
			Result := Date_time_tools.Months_text
		end

	zero: like Current
			-- Neutral element for "+" and "-"
		require -- from  GROUP_ELEMENT
			True
		do
			create Result.make_by_days (0)
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
		ensure then
			definite: Result.definite
		end
	
feature -- Comparison

	frozen deep_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void
			-- or attached to isomorphic object structures?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_deep_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			shallow_implies_deep: standard_equal (a, b) implies Result
			both_or_none_void: (a = Void) implies (Result = (b = Void))
			same_type: (Result and (a /= Void)) implies (b /= Void and then a.same_type (b))
			symmetric: Result implies deep_equal (b, a)
		end

	frozen equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached
			-- to objects considered equal?
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.is_equal (b))
		end

	frozen is_deep_equal (other: DATE_DURATION): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			shallow_implies_deep: standard_is_equal (other) implies Result
			same_type: Result implies same_type (other)
			symmetric: Result implies other.is_deep_equal (Current)
		end

	is_equal (other: like Current): BOOLEAN
			-- Are the current object and other equal?
		require -- from ANY
			other_not_void: other /= Void
		do
			Result := year = other.year and then month = other.month and then day = other.day
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result
		ensure then
			result_definition: Result = (year = other.year and then month = other.month and then day = other.day)
		end

	is_greater alias ">" (other: DATE_DURATION): BOOLEAN
			-- Is current object greater than other?
			-- (from PART_COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= Void
		do
			Result := other < Current
		end

	is_greater_equal alias ">=" (other: DATE_DURATION): BOOLEAN
			-- Is current object greater than or equal to other?
			-- (from PART_COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= Void
		do
			Result := (other < Current) or (Current ~ other)
		end

	is_less alias "<" (other: like Current): BOOLEAN
			-- Is the current object smaller than other?
			-- It is impossible to compare not definite duration.
		require -- from PART_COMPARABLE
			other_exists: other /= Void
		do
			if definite and then other.definite then
				Result := day < other.day
			else
				Result := False
			end
		ensure then
			definite_duration: (definite and then other.definite) implies Result = (day < other.day)
			non_definite_duration: (not definite or else not other.definite) implies not Result
		end

	is_less_equal alias "<=" (other: DATE_DURATION): BOOLEAN
			-- Is current object less than or equal to other?
			-- (from PART_COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= Void
		do
			Result := (Current < other) or (Current ~ other)
		end

	frozen standard_equal (a: detachable ANY; b: like arg #1): BOOLEAN
			-- Are a and b either both void or attached to
			-- field-by-field identical objects of the same type?
			-- Always uses default object comparison criterion.
			-- (from ANY)
		do
			if a = Void then
				Result := b = Void
			else
				Result := b /= Void and then a.standard_is_equal (b)
			end
		ensure -- from ANY
			instance_free: class
			definition: Result = (a = Void and b = Void) or else ((a /= Void and b /= Void) and then a.standard_is_equal (b))
		end

	frozen standard_is_equal (other: DATE_DURATION): BOOLEAN
			-- Is other attached to an object of the same type
			-- as current object, and field-by-field identical to it?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)
		end
	
feature -- Status report

	canonical (date: DATE): BOOLEAN
			-- Is duration expressed minimally for adding to date, i.e.
			-- 	If addition will yield a date after date, then:
			--		year positive,
			--		month between 0 and Months_in_year - 1,
			--		day between 0 and (number of days of the month before
			--		the yielded) - 1?
			-- 	If addition will yield a date before date, then:
			--		year negative,
			--		month between 1 - Months_in_year and 0,
			--		day between (number of days of the month before the
			--		yielded) and 0?
		require
			date_exist: date /= Void
		local
			final_date, limit_date: DATE
			d: DATE_DURATION
		do
			final_date := date + Current
			if final_date >= date then
				create d.make (year, month + 1, 0)
				limit_date := date + d
				Result := year >= 0 and then month >= 0 and then month < Months_in_year and then day >= 0 and then final_date < limit_date
			else
				create d.make (year, month - 1, 0)
				limit_date := date + d
				Result := year <= 0 and then month <= 0 and then month > - Months_in_year and then day <= 0 and then final_date > limit_date
			end
		end

	conforms_to (other: ANY): BOOLEAN
			-- Does type of current object conform to type
			-- of other (as per Eiffel: The Language, chapter 13)?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		end

	definite: BOOLEAN
			-- Is the duration is independent of the date
			-- on which it applies? (use of day only)?
			-- or not (use of year, month and day)?
		do
			Result := (year = 0) and then (month = 0)
		ensure
			result_definition: Result = ((year = 0) and then (month = 0))
		end

	has_origin_date: BOOLEAN
			-- Has origin date been set?
		do
			Result := attached origin_date
		end

	i_th_leap_year (i: INTEGER_32): BOOLEAN
		obsolete "Use `is_leap_year' instead. [2017-05-31]"
			-- (from DATE_CONSTANTS)
		do
			Result := is_leap_year (i)
		end

	is_leap_year (y: INTEGER_32): BOOLEAN
			-- Is year y a leap year?
			-- (from DATE_CONSTANTS)
		do
			Result := (mod (y, 4) = 0) and ((mod (y, 100) /= 0) or (mod (y, 400) = 0))
		end

	is_negative: BOOLEAN
			-- Is duration negative?
			-- (from DURATION)
		do
			Result := not is_positive and not is_zero
		end

	is_positive: BOOLEAN
			-- Is duration positive?
		do
			Result := day > 0 or month > 0 or year > 0
		end

	is_zero: BOOLEAN
			-- Is duration zero?
			-- (from DURATION)
		do
			Result := equal (Current, zero)
		end

	same_type (other: ANY): BOOLEAN
			-- Is type of current object identical to type of other?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))
		end
	
feature -- Status setting

	set_origin_date (d: detachable DATE)
			-- Set origin_date to d.
		do
			origin_date := d
		ensure
			origin_date_set: origin_date = d
		end
	
feature -- Element change

	identity alias "+": DATE_DURATION
			-- Unary plus
			-- (from DURATION)
		do
			Result := deep_twin
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
			result_definition: Result.is_equal (Current)
		end

	minus alias "-" (other: DATE_DURATION): DATE_DURATION
			-- Difference with other
			-- (from DURATION)
		require -- from GROUP_ELEMENT
			other_exists: other /= Void
		do
			Result := Current + - other
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
		end
	
feature -- Conversion

	to_canonical (start_date: DATE): like Current
			-- A new duration, equivalent to current one
			-- and canonical for date
		require
			start_date_not_void: start_date /= Void
		local
			date_tmp, final_date: DATE
			d1: INTEGER_32
		do
			if canonical (start_date) then
				Result := deep_twin
			else
				final_date := start_date + Current
				d1 := (final_date.year - start_date.year) * Months_in_year + final_date.month - start_date.month
				date_tmp := start_date.twin
				date_tmp.month_add (d1)
				if final_date >= start_date then
					if date_tmp <= final_date then
						create Result.make (d1 // Months_in_year, d1 \\ Months_in_year, final_date.day - date_tmp.day)
					else
						d1 := d1 - 1
						date_tmp.month_back
						if start_date.days_in_i_th_month (date_tmp.month, date_tmp.year) < start_date.day then
							create Result.make (d1 // Months_in_year, d1 \\ Months_in_year, final_date.day)
						else
							create Result.make (d1 // Months_in_year, d1 \\ Months_in_year, final_date.day + start_date.days_in_i_th_month (date_tmp.month, date_tmp.year) - start_date.day)
						end
					end
				else
					if date_tmp >= final_date then
						create Result.make (d1 // Months_in_year, d1 \\ Months_in_year, final_date.day - date_tmp.day)
					else
						d1 := d1 + 1
						date_tmp.month_forth
						create Result.make (d1 // Months_in_year, d1 \\ Months_in_year, final_date.day - start_date.days_in_i_th_month (final_date.month, final_date.year) - date_tmp.day)
					end
				end
			end
		ensure
			canonical_result: Result.canonical (start_date)
			duration_not_changed: equal (start_date + Current, start_date + Result)
		end

	to_date_time: DATE_TIME_DURATION
			-- Date-time version, with a zero time component
		do
			create Result.make (year, month, day, 0, 0, 0)
		ensure
			result_exists: Result /= Void
			year_set: Result.year = year
			month_set: Result.month = month
			day_set: Result.day = day
		end

	to_definite (date: DATE)
			-- Make current duration definite.
		require
			date_exists: date /= Void
		do
			make_by_days ((date + Current).days - date.days)
		ensure
			definite_result: definite
		end
	
feature -- Duplication

	frozen clone (other: detachable ANY): like other
		obsolete "Use `twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- equal to other
			--
			-- For non-void other, clone calls copy;
			-- to change copying/cloning semantics, redefine copy.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.twin
			end
		ensure -- from ANY
			instance_free: class
			equal: Result ~ other
		end

	copy (other: DATE_DURATION)
			-- Update current object using fields of object attached
			-- to other, so as to yield equal objects.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_equal: Current ~ other
		end

	frozen deep_clone (other: detachable ANY): like other
		obsolete "Use `deep_twin' instead. [2017-05-31]"
			-- Void if other is void: otherwise, new object structure
			-- recursively duplicated from the one attached to other
			-- (from ANY)
		do
			if other /= Void then
				Result := other.deep_twin
			end
		ensure -- from ANY
			instance_free: class
			deep_equal: deep_equal (other, Result)
		end

	frozen deep_copy (other: DATE_DURATION)
			-- Effect equivalent to that of:
			--		copy (other . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		do
			copy (other.deep_twin)
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)
		end

	frozen deep_twin: DATE_DURATION
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)
		end

	frozen standard_clone (other: detachable ANY): like other
		obsolete "Use `standard_twin' instead. [2017-05-31]"
			-- Void if other is void; otherwise new object
			-- field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		do
			if other /= Void then
				Result := other.standard_twin
			end
		ensure -- from ANY
			instance_free: class
			equal: standard_equal (Result, other)
		end

	frozen standard_copy (other: DATE_DURATION)
			-- Copy every field of other onto corresponding field
			-- of current object.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		external
			"built_in"
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)
		end

	frozen standard_twin: DATE_DURATION
			-- New object field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)
		end

	frozen twin: DATE_DURATION
			-- New object equal to Current
			-- twin calls copy; to change copying/twinning semantics, redefine copy.
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result ~ Current
		end
	
feature -- Basic operations

	frozen as_attached: attached DATE_DURATION
		obsolete "Remove calls to this feature. [2017-05-31]"
			-- Attached version of Current.
			-- (Can be used during transitional period to convert
			-- non-void-safe classes to void-safe ones.)
			-- (from ANY)
		do
			Result := Current
		end

	frozen default: detachable DATE_DURATION
			-- Default value of object's type
			-- (from ANY)
		do
		end

	frozen default_pointer: POINTER
			-- Default value of type POINTER
			-- (Avoid the need to write p.default for
			-- some p of type POINTER.)
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end

	default_rescue
			-- Process exception for routines with no Rescue clause.
			-- (Default: do nothing.)
			-- (from ANY)
		do
		end

	frozen do_nothing
			-- Execute a null action.
			-- (from ANY)
		do
		ensure -- from ANY
			instance_free: class
		end

	opposite alias "-": like Current
			-- Unary minus
		require -- from  GROUP_ELEMENT
			True
		local
			l_origin: like origin_date
		do
			create Result.make (- year, - month, - day)
			l_origin := origin_date
			if l_origin /= Void then
				Result.set_origin_date (l_origin.twin)
			else
				Result.set_origin_date (Void)
			end
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
			result_definition: (Result + Current).is_equal (zero)
		ensure then
			origin_equal: equal (origin_date, Result.origin_date)
		end

	plus alias "+" (other: like Current): like Current
			-- Sum of current object with other
		require -- from GROUP_ELEMENT
			other_exists: other /= Void
		local
			l_origin: like origin_date
		do
			create Result.make (year + other.year, month + other.month, day + other.day)
			l_origin := origin_date
			if l_origin /= Void then
				Result.set_origin_date (l_origin.twin)
			else
				Result.set_origin_date (Void)
			end
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
			commutative: Result.is_equal (other + Current)
		ensure then
			origin_equal: equal (origin_date, Result.origin_date)
		end
	
feature {NONE} -- Basic operations

	div (i, j: INTEGER_32): INTEGER_32
			-- (i \\ j) if i positive
			-- (i \\ j + 1) if i negative
			-- (from TIME_UTILITY)
		do
			Result := i // j
			if Result.to_double > i / j then
				Result := Result - 1
			end
		ensure -- from TIME_UTILITY
			result_definition: i = j * Result + mod (i, j)
		end

	mod (i, j: INTEGER_32): INTEGER_32
			-- (i \\ j) if i positive
			-- (i \\ j + j) if i negative
			-- (from TIME_UTILITY)
		do
			Result := i \\ j
			if Result < 0 then
				Result := Result + j
			end
		ensure -- from TIME_UTILITY
			positive_result: Result >= 0
			result_definition: i = j * div (i, j) + Result
		end
	
feature {NONE} -- Implementation

	Days_in_months: ARRAY [INTEGER_32]
			-- Array containing number of days for each month of
			-- a non-leap year.
			-- (from DATE_CONSTANTS)
		once
			Result := <<31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31>>
		ensure -- from DATE_CONSTANTS
			result_exists: Result /= Void
			valid_count: Result.count = Months_in_year
		end
	
feature -- Attribute

	day: INTEGER_32
			-- Number of days associated with current object

	days_count: INTEGER_32
			-- Number of days in duration
		require
			origin_date_set: has_origin_date
		do
			check
				origin_date_not_void: attached origin_date as l_origin_date
			then
				Result := (l_origin_date + to_canonical (l_origin_date)).days - l_origin_date.days
			end
		end

	month: INTEGER_32
			-- Number of monthes associated with current object

	origin_date: detachable DATE
			-- Origin date of duration

	year: INTEGER_32
			-- Number of years associated with current object
	
feature -- Element Change

	day_add (d: INTEGER_32)
			-- Add d days to Current.
		do
			day := day + d
		ensure
			day_set: day = old day + d
		end

	month_add (m: INTEGER_32)
			-- Add m months to Current.
		do
			month := month + m
		ensure
			month_set: month = old month + m
		end

	set_date (y, m, d: INTEGER_32)
			-- Set year with y, month with m and day with d.
		require -- from DATE_MEASUREMENT
			d_large_enough: d >= 1
			m_large_enough: m >= 1
			m_small_enough: m <= Months_in_year
			d_small_enough: d <= days_in_i_th_month (m, y)
		do
			day := d
			month := m
			year := y
		ensure -- from DATE_MEASUREMENT
			day_set: day = d
			month_set: month = m
			year_set: year = y
		end

	set_day (d: INTEGER_32)
			-- Set day to d.
		require -- from DATE_MEASUREMENT
			d_large_enough: d >= 1
			d_small_enough: d <= days_in_month
		do
			day := d
		ensure -- from DATE_MEASUREMENT
			day_set: day = d
		end

	set_month (m: INTEGER_32)
			-- Set month to m.
		require -- from DATE_MEASUREMENT
			m_large_enough: m >= 1
			m_small_enough: m <= Months_in_year
			d_small_enough: day <= days_in_i_th_month (m, year)
		do
			month := m
		ensure -- from DATE_MEASUREMENT
			month_set: month = m
		end

	set_year (y: INTEGER_32)
			-- Set year to y.
		require -- from DATE_MEASUREMENT
			can_not_cut_29th_feb: day <= days_in_i_th_month (month, y)
		do
			year := y
		ensure -- from DATE_MEASUREMENT
			year_set: year = y
		end

	year_add (y: INTEGER_32)
			-- Add y years to Current.
		do
			year := year + y
		ensure
			year_set: year = old year + y
		end
	
feature -- Output

	Io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)
		once
			create Result
			Result.set_output_default
		ensure -- from ANY
			instance_free: class
			io_not_void: Result /= Void
		end

	out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		do
			Result := tagged_out
		ensure -- from ANY
			out_not_void: Result /= Void
		end

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		do
			if o /= Void then
				Io.put_string (o.out)
			end
		ensure -- from ANY
			instance_free: class
		end

	frozen tagged_out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- (from ANY)
		external
			"built_in"
		ensure -- from ANY
			tagged_out_not_void: Result /= Void
		end
	
feature -- Platform

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		once
			create Result
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
		end
	
feature {NONE} -- Retrieval

	frozen internal_correct_mismatch
			-- Called from runtime to perform a proper dynamic dispatch on correct_mismatch
			-- from MISMATCH_CORRECTOR.
			-- (from ANY)
		local
			l_msg: STRING_8
			l_exc: EXCEPTIONS
		do
			if attached {MISMATCH_CORRECTOR} Current as l_corrector then
				l_corrector.correct_mismatch
			else
				create l_msg.make_from_string ("Mismatch: ")
				create l_exc
				l_msg.append (generating_type.name)
				l_exc.raise_retrieval_exception (l_msg)
			end
		end
	
feature -- Status Report

	days_in_month: INTEGER_32
			-- Number of days in month 'month'.
			-- (from DATE_MEASUREMENT)
		do
			Result := days_in_i_th_month (month, year)
		ensure -- from DATE_MEASUREMENT
			positive_result: Result > 0
		end
	
invariant
	equal_signs: (has_origin_date and then attached origin_date as l_origin_date and then canonical (l_origin_date)) implies (day >= 0 and month >= 0 and year >= 0) or (day <= 0 and month <= 0 and year <= 0)

		-- from DURATION
	sign_correctness: is_positive xor is_negative xor is_zero

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

		-- from GROUP_ELEMENT
	neutral_addition: is_equal (Current + zero)
	self_subtraction: zero.is_equal (Current - Current)

note
	copyright: "Copyright (c) 1984-2017, 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 DATE_DURATION

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