note
	description: "External forward iteration cursor for descendants of {LINKED_TREE}."

class interface
	LINKED_TREE_ITERATION_CURSOR [G]

create {LINKED_TREE}
	make (t: like node)
			-- Initialize the cursor with a target tree target.
		require -- from  TREE_ITERATION_CURSOR
			True
		require -- from READABLE_INDEXABLE_ITERATION_CURSOR
			t_attached: attached t
		ensure -- from TREE_ITERATION_CURSOR
			node_set: node = t
			child_index_set: child_index.count = 1 and then child_index.item = 0
		ensure -- from READABLE_INDEXABLE_ITERATION_CURSOR
			target_set: target = t
			is_valid: is_valid
			default_step: step = 1
			ascending_traversal: not is_reversed

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
		ensure -- from INDEXABLE_ITERATION_CURSOR
			positive_index: Result >= 0

	decremented alias "-" (n: like step): LINKED_TREE_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
		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

	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 LINKED_TREE_ITERATION_CURSOR [G]]
			-- Type of current object
			-- (type of which it is a direct instance)
			-- (from ANY)
		ensure -- from ANY
			generating_type_not_void: Result /= Void

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

	incremented alias "+" (n: like step): LINKED_TREE_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
		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

	item: G
			-- Item at current cursor position.
			-- (from TREE_ITERATION_CURSOR)
		require -- from ITERATION_CURSOR
			valid_position: not after

	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: LINKED_TREE_ITERATION_CURSOR [G]
			-- Restarted cursor of the iteration.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from  ITERABLE
			True
		ensure -- from ITERABLE
			result_attached: Result /= Void

	reversed alias "-": LINKED_TREE_ITERATION_CURSOR [G]
			-- Reversed cursor of the iteration.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		require -- from  INDEXABLE_ITERATION_CURSOR
			True
		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

	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): LINKED_TREE_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
		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
	
feature -- Measurement

	version: NATURAL_32
			-- Current version.
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)
		note
			option: transient
	
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)
		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)

	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)
		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))

	frozen is_deep_equal alias "≡≡≡" (other: LINKED_TREE_ITERATION_CURSOR [G]): BOOLEAN
			-- Are Current and other attached to isomorphic object structures?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		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)

	is_equal (other: LINKED_TREE_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
		ensure -- from ANY
			symmetric: Result implies other ~ Current
			consistent: standard_is_equal (other) implies Result

	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)
		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))

	frozen standard_is_equal alias "≜" (other: LINKED_TREE_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
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)
	
feature -- Status report

	after: BOOLEAN
			-- Are there no more items to iterate over?
			-- (from TREE_ITERATION_CURSOR)
		require -- from  ITERATION_CURSOR
			True

	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

	is_first: BOOLEAN
			-- Is cursor at first position?
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	is_last: BOOLEAN
			-- Is cursor at last position?
			-- (from READABLE_INDEXABLE_ITERATION_CURSOR)

	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)

	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
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))
	
feature -- Status setting

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

	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
		ensure -- from READABLE_INDEXABLE_ITERATION_CURSOR
			step_set: step = v
	
feature -- Cursor movement

	forth
			-- Move to next position.
		require -- from ITERATION_CURSOR
			valid_position: not after
		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

	start
			-- Move to first position.
		require -- from  INDEXABLE_ITERATION_CURSOR
			True
		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
	
feature -- Duplication

	copy (other: LINKED_TREE_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)
		ensure -- from ANY
			is_equal: Current ~ other

	frozen deep_copy (other: LINKED_TREE_ITERATION_CURSOR [G])
			-- Effect equivalent to that of:
			--		copy (other . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)

	frozen deep_twin: LINKED_TREE_ITERATION_CURSOR [G]
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		ensure -- from ANY
			deep_twin_not_void: Result /= Void
			deep_equal: deep_equal (Current, Result)

	frozen standard_copy (other: LINKED_TREE_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)
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)

	frozen standard_twin: LINKED_TREE_ITERATION_CURSOR [G]
			-- New object field-by-field identical to other.
			-- Always uses default copying semantics.
			-- (from ANY)
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)

	frozen twin: LINKED_TREE_ITERATION_CURSOR [G]
			-- New object equal to Current
			-- twin calls copy; to change copying/twinning semantics, redefine copy.
			-- (from ANY)
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result ~ Current
	
feature -- Basic operations

	frozen default: detachable LINKED_TREE_ITERATION_CURSOR [G]
			-- Default value of object's type
			-- (from ANY)

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

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

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

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

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

	print (o: detachable ANY)
			-- Write terse external representation of o
			-- on standard output.
			-- (from ANY)
		ensure -- from ANY
			instance_free: class

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

	Operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
		ensure -- from ANY
			instance_free: class
			operating_environment_not_void: Result /= Void
	
invariant
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

		-- from INDEXABLE_ITERATION_CURSOR
	step_positive: step > 0

note
	library: "EiffelBase: Library of reusable components for Eiffel."
	date: "$Date: 2018-11-30 11:40:30 +0000 (Fri, 30 Nov 2018) $"
	revision: "$Revision: 102548 $"
	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 LINKED_TREE_ITERATION_CURSOR

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