note
	description: "Concrete of an external iteration cursor for {TWO_WAY_LIST}."
	library: "EiffelBase: Library of reusable components for Eiffel."
	status: "See notice at end of class."
	legal: "See notice at end of class."
	copyright: "Copyright (c) 1984-2011, Eiffel Software and others"
	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
	date: "$Date: 2016-03-02 21:15:09 +0000 (Wed, 02 Mar 2016) $"
	revision: "$Revision: 98557 $"

class 
	TWO_WAY_LIST_ITERATION_CURSOR [G]

create 
	make

feature {NONE} -- Initialization

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

	make (t: like target)
			-- Initialize cursor for target t.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from READABLE_INDEXABLE_ITERATION_CURSOR
			t_attached: attached t
		do
			target := t
			if attached {VERSIONABLE} t as l_versionable then
				version := l_versionable.version
			else
				version := 0
			end
			step := 1
			is_reversed := False
		ensure -- from READABLE_INDEXABLE_ITERATION_CURSOR
			target_set: target = t
			is_valid: is_valid
			default_step: step = 1
			ascending_traversal: not is_reversed
		end
	
feature -- Access

	cursor_index: INTEGER_32
			-- Index position of cursor in the iteration.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from INDEXABLE_ITERATION_CURSOR
			is_valid: is_valid
		do
			Result := ((target_index - first_index).abs + step - 1) // step + 1
		ensure -- from INDEXABLE_ITERATION_CURSOR
			positive_index: Result >= 0
		end

	decremented alias "-" (n: like step): TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- Cursor for the iteration with step decreased by n.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from INDEXABLE_ITERATION_CURSOR
			n_valid: step > n
		do
			Result := twin;
			Result.set_step (step - n)
		ensure -- from INDEXABLE_ITERATION_CURSOR
			is_incremented: Result.step = step - n
			same_direction: Result.is_reversed = is_reversed
		ensure then -- from TYPED_INDEXABLE_ITERATION_CURSOR
			same_target: Result.target = target
		end

	first_index: INTEGER_32
			-- First valid index of target structure for current iteration.
			-- Note that if is_reversed, first_index might be greater than last_index.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	generating_type: TYPE [detachable TWO_WAY_LIST_ITERATION_CURSOR [G]]
			-- 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

	incremented alias "+" (n: like step): TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- Cursor for the iteration with step increased by n.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from INDEXABLE_ITERATION_CURSOR
			n_valid: step + n > 0
		do
			Result := twin;
			Result.set_step (step + n)
		ensure -- from INDEXABLE_ITERATION_CURSOR
			is_incremented: Result.step = step + n
			same_direction: Result.is_reversed = is_reversed
		ensure then -- from TYPED_INDEXABLE_ITERATION_CURSOR
			same_target: Result.target = target
		end

	item: G
			-- Item at current cursor position.
		require -- from ITERATION_CURSOR
			valid_position: not after
		do
			check
				active_attached: attached active as a
			then
				Result := a.item
			end
		end

	last_index: INTEGER_32
			-- Last valid index of target structure for current iteration.
			-- Note that if is_reversed, first_index might be greater than last_index.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	new_cursor: TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- Restarted cursor of the iteration.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from  ITERABLE
			True
		do
			Result := twin;
			Result.start
		ensure -- from ITERABLE
			result_attached: Result /= Void
		end

	reversed alias "-": TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- Reversed cursor of the iteration.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from  INDEXABLE_ITERATION_CURSOR
			True
		do
			Result := twin;
			Result.reverse
		ensure -- from INDEXABLE_ITERATION_CURSOR
			is_reversed: Result.is_reversed = not is_reversed
			same_step: Result.step = step
		ensure then -- from TYPED_INDEXABLE_ITERATION_CURSOR
			same_target: Result.target = target
		end

	step: INTEGER_32
			-- Distance between successive iteration elements.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	target_index: INTEGER_32
			-- Index position of target structure for current iteration.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	with_step (n: like step): TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- Cursor for the iteration with step set to n.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from INDEXABLE_ITERATION_CURSOR
			n_positive: n > 0
		do
			Result := twin;
			Result.set_step (n)
		ensure -- from INDEXABLE_ITERATION_CURSOR
			step_set: Result.step = n
			same_direction: Result.is_reversed = is_reversed
		ensure then -- from TYPED_INDEXABLE_ITERATION_CURSOR
			same_target: Result.target = target
		end
	
feature {ITERABLE, ITERATION_CURSOR}{ITERABLE, ITERATION_CURSOR}{TYPED_INDEXABLE_ITERATION_CURSOR}{TYPED_INDEXABLE_ITERATION_CURSOR} -- Access

	target: TWO_WAY_LIST [G]
			-- Associated structure used for iteration.
	
feature {NONE} -- Access

	active: detachable BI_LINKABLE [G]
			-- Currrently active linkable node for ascending traversal
	
feature -- Measurement

	version: NATURAL_32
			-- Current version.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		note
			option: transient
		attribute
		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 alias "≡≡≡" (other: TWO_WAY_LIST_ITERATION_CURSOR [G]): 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: TWO_WAY_LIST_ITERATION_CURSOR [G]): BOOLEAN
			-- Is other attached to an object considered
			-- equal to current object?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		external
			"built_in"
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result
		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 alias "≜" (other: TWO_WAY_LIST_ITERATION_CURSOR [G]): 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

	after: BOOLEAN
			-- Are there no more items to iterate over?
		require -- from  ITERATION_CURSOR
			True
		do
			Result := not is_valid or active = Void
		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

	is_first: BOOLEAN
			-- Is cursor at first position?
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		do
			Result := target_index = first_index and then is_valid
		end

	is_last: BOOLEAN
			-- Is cursor at last position?
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		do
			Result := target_index = last_index and then is_valid
		end

	is_reversed: BOOLEAN
			-- Are we traversing target structure backwards?
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	is_valid: BOOLEAN
			-- Is the cursor still compatible with the associated underlying object?
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		do
			Result := attached {VERSIONABLE} target as l_versionable implies l_versionable.version = version
		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

	reverse
			-- Flip traversal order.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		do
			is_reversed := not is_reversed
		ensure -- from READABLE_INDEXABLE_ITERATION_CURSOR
			is_reversed: is_reversed = not old is_reversed
		end

	set_step (v: like step)
			-- Set increment step to v.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from READABLE_INDEXABLE_ITERATION_CURSOR
			v_positive: v > 0
		do
			step := v
		ensure -- from READABLE_INDEXABLE_ITERATION_CURSOR
			step_set: step = v
		end
	
feature -- Cursor movement

	forth
			-- Move to next position.
		require -- from ITERATION_CURSOR
			valid_position: not after
		local
			i: like step
		do
			if is_reversed then
				target_index := target_index - step
				from
					i := 1
				until
					i > step or else not attached active as l_active
				loop
					active := l_active.left
					i := i + 1
				end
			else
				target_index := target_index + step
				from
					i := 1
				until
					i > step or else not attached active as l_active
				loop
					active := l_active.right
					i := i + 1
				end
			end
		ensure then -- from INDEXABLE_ITERATION_CURSOR
			cursor_index_advanced: cursor_index = old cursor_index + 1
		ensure then -- from READABLE_INDEXABLE_ITERATION_CURSOR
			cursor_index_advanced: cursor_index = old cursor_index + 1
		end

	start
			-- Move to first position.
		require -- from  INDEXABLE_ITERATION_CURSOR
			True
		local
			l_list: like target
		do
			l_list := target
			if is_reversed then
				first_index := l_list.count
				last_index := l_list.Lower
			else
				last_index := l_list.count
				first_index := l_list.Lower
			end
			target_index := first_index
			if is_reversed then
				active := l_list.last_element
			else
				active := l_list.first_element
			end
		ensure -- from INDEXABLE_ITERATION_CURSOR
			cursor_index_set_to_one: cursor_index = 1
			target_index_set_to_first: target_index = first_index
			is_first: is_first
		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: TWO_WAY_LIST_ITERATION_CURSOR [G])
			-- 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: TWO_WAY_LIST_ITERATION_CURSOR [G])
			-- 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: TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- 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: TWO_WAY_LIST_ITERATION_CURSOR [G])
			-- 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: TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- 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: TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- 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 TWO_WAY_LIST_ITERATION_CURSOR [G]
		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 TWO_WAY_LIST_ITERATION_CURSOR [G]
			-- 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
	
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)
		local
			s: READABLE_STRING_8
		do
			if attached o then
				s := o.out
				if attached {READABLE_STRING_32} s as s32 then
					Io.put_string_32 (s32)
				elseif attached {READABLE_STRING_8} s as s8 then
					Io.put_string (s8)
				else
					Io.put_string_32 (s.as_string_32)
				end
			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_32
			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: ".as_string_32)
				create l_exc;
				l_msg.append (generating_type.name_32);
				l_exc.raise_retrieval_exception (l_msg)
			end
		end
	
invariant
		-- from INDEXABLE_ITERATION_CURSOR
	step_positive: step > 0

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

note
	copyright: "Copyright (c) 1984-2016, 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 TWO_WAY_LIST_ITERATION_CURSOR

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