note
	description: "Sorted sets implemented as binary search trees"
	library: "Free implementation of ELKS library"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	names: binary_search_tree_set, set, binary_search_tree
	representation: recursive, array
	access: membership, min, max
	contents: generic
	date: "$Date: 2019-07-05 15:26:16 +0000 (Fri, 05 Jul 2019) $"
	revision: "$Revision: 103325 $"

class 
	BINARY_SEARCH_TREE_SET [G -> COMPARABLE]

create 
	make,
	make_from_iterable

feature {NONE} -- Initialization

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

	make
			-- Create set.
		do
			before := True
		end

	make_from_iterable (other: ITERABLE [G])
			-- Create a set with all items obtained from other.
		do
			make
			across
				other as o
			loop
				extend (o.item)
			end
		end
	
feature -- Access

	generating_type: TYPE [detachable BINARY_SEARCH_TREE_SET [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

	index_of (v: like item; i: INTEGER_32): INTEGER_32
			-- Index of i-th occurrence of v.
			-- 0 if none.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		require -- from LINEAR
			positive_occurrences: i > 0
		local
			occur, pos: INTEGER_32
		do
			if object_comparison and v /= Void then
				from
					start
					pos := 1
				until
					exhausted or (occur = i)
				loop
					if item ~ v then
						occur := occur + 1
					end
					forth
					pos := pos + 1
				end
			else
				from
					start
					pos := 1
				until
					exhausted or (occur = i)
				loop
					if item = v then
						occur := occur + 1
					end
					forth
					pos := pos + 1
				end
			end
			if occur = i then
				Result := pos - 1
			end
		ensure -- from LINEAR
			non_negative_result: Result >= 0
		end

	item_for_iteration: G
			-- Item at current position
			-- (from LINEAR)
		require -- from LINEAR
			not_off: not off
		do
			Result := item
		end

	occurrences (v: like item): INTEGER_32
			-- Number of times v appears.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from LINEAR)
		do
			from
				start
				search (v)
			until
				exhausted
			loop
				Result := Result + 1
				forth
				search (v)
			end
		end
	
feature -- Measurement

	count: INTEGER_32
			-- Number of items in tree
		require -- from  SET
			True
		local
			t: like tree
		do
			t := tree
			if t /= Void then
				Result := t.count
			end
		end

	item: G
			-- Current item
		require -- from TRAVERSABLE
			not_off: not off
		require -- from TRAVERSABLE_SUBSET
			not_off: not off
		do
			check
					attached active_node as a
			then
				Result := a.item
			end
		end

	cs_max: like item
			-- Maximum item
			-- (from COMPARABLE_STRUCT)
		require -- from COMPARABLE_STRUCT
				min_max_available
		do
			from
				start
				Result := item
				forth
			until
				off
			loop
				if item > Result then
					Result := item
				end
				forth
			end
		end

	max: like item
			-- Maximum item in tree
		require -- from COMPARABLE_SET
			not_empty: not is_empty
		do
			check
					attached tree as t
			then
				Result := t.max
			end
		end

	min: like item
			-- Minimum item in tree
		require -- from COMPARABLE_SET
			not_empty: not is_empty
		do
			check
					attached tree as t
			then
				Result := t.min
			end
		end

	cs_min: like item
			-- Minimum item
			-- (from COMPARABLE_STRUCT)
		require -- from COMPARABLE_STRUCT
				min_max_available
		do
			from
				start
				Result := item
				forth
			until
				off
			loop
				if item < Result then
					Result := item
				end
				forth
			end
		end

	min_max_available: BOOLEAN
			-- Can min and max be computed?
			-- (from COMPARABLE_STRUCT)
		do
			Result := not is_empty
		ensure -- from COMPARABLE_STRUCT
				Result implies not is_empty
		end
	
feature {NONE} -- Measurement

	estimated_count_of (other: ITERABLE [G]): INTEGER_32
			-- Estimated number of elements in other.
			-- (from CONTAINER)
		do
			if attached {FINITE [G]} other as f then
				Result := f.count
			elseif attached {READABLE_INDEXABLE [G]} other as r then
				Result := r.upper - r.lower + 1
			end
		ensure -- from CONTAINER
			instance_free: class
			non_negative_result: Result >= 0
		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

	disjoint (other: TRAVERSABLE_SUBSET [G]): BOOLEAN
			-- Do current set and other have no
			-- items in common?
			-- (from TRAVERSABLE_SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		do
			if not is_empty and not other.is_empty then
				Result := subset_strategy (other).disjoint (Current, other)
			else
				Result := True
			end
		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: BINARY_SEARCH_TREE_SET [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: BINARY_SEARCH_TREE_SET [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

	is_subset alias "⊆" (other: TRAVERSABLE_SUBSET [G]): BOOLEAN
			-- Is current set a subset of other?
			-- (from TRAVERSABLE_SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		do
			if not other.is_empty and then count <= other.count then
				from
					start
				until
					off or else not (other ∋ item)
				loop
					forth
				end
				if off then
					Result := True
				end
			elseif is_empty then
				Result := True
			end
		end

	is_superset alias "⊇" (other: SUBSET [G]): BOOLEAN
			-- Is current set a superset of other?
			-- (from SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		do
			Result := other ⊆ Current
		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: BINARY_SEARCH_TREE_SET [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
			-- Is there no valid cursor position to the right of cursor?

	before: BOOLEAN
			-- Is there no valid cursor position to the left of cursor?

	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

	empty: BOOLEAN
		obsolete "ELKS 2000: Use `is_empty' instead. [2017-05-31]"
			-- Is there no element?
			-- (from CONTAINER)
		do
			Result := is_empty
		end

	exhausted: BOOLEAN
			-- Has structure been completely explored?
			-- (from LINEAR)
		do
			Result := off
		ensure -- from LINEAR
			exhausted_when_off: off implies Result
		end

	Extendible: BOOLEAN = True
			-- Can new items be added? (Answer: yes.)

	has alias "∋" (v: like item): BOOLEAN
			-- Is there a node with item v in tree?
			-- (Reference or object equality,
			-- based on object_comparison.)
		require -- from  CONTAINER
			True
		local
			t: like tree
		do
			t := tree
			if t /= Void then
				Result := t.has (v)
			end
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty
		end

	is_empty: BOOLEAN
			-- Is set empty?
		require -- from  CONTAINER
			True
		do
			Result := tree = Void
		end

	is_inserted (v: G): BOOLEAN
			-- Has v been inserted by the most recent insertion?
			-- (By default, the value returned is equivalent to calling 
			-- has (v). However, descendants might be able to provide more
			-- efficient implementations.)
			-- (from COLLECTION)
		do
			Result := has (v)
		end

	object_comparison: BOOLEAN
			-- Must search operations use equal rather than =
			-- for comparing references? (Default: no, use =.)
			-- (from CONTAINER)

	off: BOOLEAN
			-- Is there no current item?
			-- off only if tree is_empty or if
			-- it is before or after.
		require -- from  TRAVERSABLE
			True
		require -- from  TRAVERSABLE_SUBSET
			True
		do
			Result := is_empty or Precursor {COMPARABLE_SET}
		end

	Prunable: BOOLEAN = True
			-- Can items be removed? (Answer: yes.)

	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

	compare_objects
			-- Ensure that future search operations will use equal
			-- rather than = for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion: changeable_comparison_criterion
		do
			object_comparison := True
		ensure -- from CONTAINER
				object_comparison
		end

	compare_references
			-- Ensure that future search operations will use =
			-- rather than equal for comparing references.
			-- (from CONTAINER)
		require -- from CONTAINER
			changeable_comparison_criterion: changeable_comparison_criterion
		do
			object_comparison := False
		ensure -- from CONTAINER
			reference_comparison: not object_comparison
		end
	
feature -- Cursor movement

	back
			-- Move cursor to previous node.
		require -- from BILINEAR
			not_before: not before
		local
			prev_node: like tree
			a: like active_node
			l: like active_node
		do
			if after then
				after := False
				if is_empty then
					before := True
				end
			else
				a := active_node
				if a /= Void then
					l := a.left_child
					if l /= Void then
						active_node := l.max_node
					else
						from
							prev_node := a
							a := a.parent
						until
							a = Void or else prev_node = a.right_child
						loop
							prev_node := a
							a := a.parent
						end
						if a = Void then
							active_node := tree
							before := True
						else
							active_node := a
						end
					end
				end
			end
		end

	finish
			-- Move cursor to last node.
		local
			t: like tree
		do
			after := False
			t := tree
			if t = Void then
				before := True
			else
				before := False
				active_node := t.max_node
			end
		end

	forth
			-- Move cursor to next node.
		require -- from LINEAR
			not_after: not after
		require -- from TRAVERSABLE_SUBSET
			not_after: not after
		local
			prev_node: like tree
			a: like active_node
			r: like active_node
		do
			if before then
				before := False
				if is_empty then
					after := True
				end
			else
				a := active_node
				if a /= Void then
					r := a.right_child
					if r /= Void then
						active_node := r.min_node
					else
						from
							prev_node := a
							a := a.parent
						until
							a = Void or else prev_node = a.left_child
						loop
							prev_node := a
							a := a.parent
						end
						if a = Void then
							active_node := tree
							after := True
						else
							active_node := a
						end
					end
				end
			end
		end

	search (v: like item)
			-- Move to first position (at or after current
			-- position) where item and v are equal.
			-- If structure does not include v ensure that
			-- exhausted will be true.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from BILINEAR)
		do
			if before and not is_empty then
				forth
			end
			Precursor (v)
		ensure -- from LINEAR
			object_found: (not exhausted and object_comparison) implies v ~ item
			item_found: (not exhausted and not object_comparison) implies v = item
		end

	start
			-- Move cursor to first node.
		require -- from  TRAVERSABLE
			True
		require -- from  TRAVERSABLE_SUBSET
			True
		local
			t: like tree
		do
			before := False
			t := tree
			if t = Void then
				after := True
			else
				after := False
				active_node := t.min_node
			end
		end
	
feature -- Element change

	extend (v: like item)
			-- Put v at proper position in set
			-- (unless one already exists).
			-- Was declared in BINARY_SEARCH_TREE_SET as synonym of put.
		require -- from COLLECTION
			extendible: Extendible
		require else
			item_exists: v /= Void
		local
			t: like tree
		do
			t := tree
			if t = Void then
				tree := new_tree (v)
			elseif not has (v) then
				t.extend (v)
			end
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from SET
			in_set_already: old has (v) implies (count = old count)
			added_to_set: not old has (v) implies (count = old count + 1)
		end

	fill (other: CONTAINER [G])
			-- Fill with as many items of other as possible.
			-- The representations of other and current structure
			-- need not be the same.
			-- (from COLLECTION)
		require -- from COLLECTION
			other_not_void: other /= Void
			extendible: Extendible
		local
			lin_rep: LINEAR [G]
		do
			lin_rep := other.linear_representation
			from
				lin_rep.start
			until
				not Extendible or else lin_rep.off
			loop
				extend (lin_rep.item);
				lin_rep.forth
			end
		end

	merge (other: CONTAINER [G])
			-- Add all items of other.
			-- (from TRAVERSABLE_SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		local
			l: LINEAR [G]
		do
			if attached {LINEAR [G]} other as lin_rep then
				l := lin_rep
			else
				l := other.linear_representation
			end
			from
				l.start
			until
				l.off
			loop
				extend (l.item);
				l.forth
			end
		end

	put (v: like item)
			-- Put v at proper position in set
			-- (unless one already exists).
			-- Was declared in BINARY_SEARCH_TREE_SET as synonym of extend.
		require -- from COLLECTION
			extendible: Extendible
		require else
			item_exists: v /= Void
		local
			t: like tree
		do
			t := tree
			if t = Void then
				tree := new_tree (v)
			elseif not has (v) then
				t.extend (v)
			end
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from SET
			in_set_already: old has (v) implies (count = old count)
			added_to_set: not old has (v) implies (count = old count + 1)
		end
	
feature -- Removal

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: only if set empty; otherwise insertions might
			-- introduce duplicates, destroying the set property.)
			-- (from SET)
		require -- from  CONTAINER
			True
		do
			Result := is_empty
		ensure then -- from SET
			only_on_empty: Result = is_empty
		end

	prune (v: like item)
			-- Remove v.
		require -- from COLLECTION
			prunable: Prunable
		local
			t: like tree
		do
			t := tree
			if t /= Void then
				tree := t.pruned (v, t.parent)
			end
		ensure then -- from SET
			removed_count_change: old has (v) implies (count = old count - 1)
			not_removed_no_count_change: not old has (v) implies (count = old count)
			item_deleted: not has (v)
		end

	prune_all (v: G)
			-- Remove all occurrences of v.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from COLLECTION)
		require -- from COLLECTION
			prunable: Prunable
		do
			from
			until
				not has (v)
			loop
				prune (v)
			end
		ensure -- from COLLECTION
			no_more_occurrences: not has (v)
		end

	remove
			-- Remove current item.
		require -- from TRAVERSABLE_SUBSET
			not_off: not off
		local
			l_item: like item
			l_next_item: detachable like item
		do
			if attached tree as t then
				l_item := item
				forth
				if not after then
					l_next_item := item
				end
				tree := t.pruned (l_item, t.parent)
				if l_next_item /= Void and attached tree as t2 then
					active_node := t2.tree_item (l_next_item)
				end
			end
		end

	wipe_out
			-- Remove all items.
		require -- from COLLECTION
			prunable: Prunable
		do
			tree := Void
		ensure -- from COLLECTION
			wiped_out: is_empty
		end
	
feature -- Conversion

	linear_representation: LINEAR [G]
			-- Representation as a linear structure
			-- (from LINEAR)
		require -- from  CONTAINER
			True
		do
			Result := Current
		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: BINARY_SEARCH_TREE_SET [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: BINARY_SEARCH_TREE_SET [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: BINARY_SEARCH_TREE_SET [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

	duplicate (n: INTEGER_32): BINARY_SEARCH_TREE_SET [G]
		obsolete "[
			Create a new container explicitly using `make_from_iterable` if available.
			Otherwise, replace a call to the feature with code that creates and initializes container.
			[2018-11-30]
		]"
			-- New structure containing min (n, count)
			-- items from current structure
		require -- from SUBSET
			non_negative: n >= 0
		local
			t: like tree
		do
			create Result.make
			t := tree
			if t /= Void then
				Result.set_tree (t.duplicate (n))
			end
		ensure -- from SUBSET
			correct_count_1: n <= count implies Result.count = n
			correct_count_2: n >= count implies Result.count = count
		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: BINARY_SEARCH_TREE_SET [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: BINARY_SEARCH_TREE_SET [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: BINARY_SEARCH_TREE_SET [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 BINARY_SEARCH_TREE_SET [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 BINARY_SEARCH_TREE_SET [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

	intersect (other: TRAVERSABLE_SUBSET [G])
			-- Remove all items not in other.
			-- No effect if other is_empty.
			-- (from TRAVERSABLE_SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		do
			if not other.is_empty then
				from
					start;
					other.start
				until
					off
				loop
					if other ∋ item then
						forth
					else
						remove
					end
				end
			else
				wipe_out
			end
		ensure -- from SUBSET
			is_subset_other: is_subset (other)
		end

	subtract (other: TRAVERSABLE_SUBSET [G])
			-- Remove all items also in other.
			-- (from TRAVERSABLE_SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		do
			if not (other.is_empty or is_empty) then
				from
					start;
					other.start
				until
					off
				loop
					if other ∋ item then
						remove
					else
						forth
					end
				end
			end
		ensure -- from SUBSET
			is_disjoint: disjoint (other)
		end

	symdif (other: TRAVERSABLE_SUBSET [G])
			-- Remove all items also in other, and add all
			-- items of other not already present.
			-- (from TRAVERSABLE_SUBSET)
		require -- from SUBSET
			set_exists: other /= Void
			same_rule: object_comparison = other.object_comparison
		do
			if not other.is_empty then
				if is_empty then
					from
						other.start
					until
						other.after
					loop
						extend (other.item)
					end
				else
					subset_strategy (other).symdif (Current, other)
				end
			end
		end
	
feature -- Inapplicable

	index: INTEGER_32
			-- Index of current position
			-- (from COMPARABLE_STRUCT)
		do
		end
	
feature {BINARY_SEARCH_TREE_SET} -- Implementation

	active_node: like tree

	set_tree (t: like tree)
			-- Set tree and active_node to t
		do
			tree := t
			active_node := t
		end

	tree: detachable BINARY_SEARCH_TREE [G]
	
feature {NONE} -- Implementation

	new_tree (v: like item): like tree
			-- New allocated node with item set to v
		do
			create Result.make (v)
			if object_comparison then
				Result.compare_objects
			end
		end

	subset_strategy (other: TRAVERSABLE_SUBSET [G]): SUBSET_STRATEGY [G]
			-- Subset strategy suitable for the type of the contained elements.
			-- (from TRAVERSABLE_SUBSET)
		require -- from TRAVERSABLE_SUBSET
			not_empty: not is_empty
		do
			start
			check
				not_off: not off
			end
			Result := subset_strategy_selection (item, other)
		end

	subset_strategy_selection (v: G; other: TRAVERSABLE_SUBSET [G]): SUBSET_STRATEGY [G]
			-- Strategy to calculate several subset features selected depending
			-- on the dynamic type of v and other
		require -- from TRAVERSABLE_SUBSET
			item_exists: v /= Void
			other_exists: other /= Void
		do
			if attached {HASHABLE} v as h then
				create {SUBSET_STRATEGY_HASHABLE [G]} Result
			elseif object_comparison and same_type (other) then
				create {SUBSET_STRATEGY_TREE [G]} Result
			else
				create {SUBSET_STRATEGY_GENERIC [G]} Result
			end
		ensure -- from TRAVERSABLE_SUBSET
			strategy_set: Result /= Void
		end
	
feature -- Iteration

	do_all (action: PROCEDURE [G])
			-- Apply action to every item.
			-- Semantics not guaranteed if action changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= Void
		local
			c: detachable CURSOR
			cs: detachable CURSOR_STRUCTURE [G]
		do
			if attached {CURSOR_STRUCTURE [G]} Current as acs then
				cs := acs
				c := acs.cursor
			end
			from
				start
			until
				after
			loop
				action.call ([item])
				forth
			end
			if cs /= Void and c /= Void then
				cs.go_to (c)
			end
		end

	do_if (action: PROCEDURE [G]; test: FUNCTION [G, BOOLEAN])
			-- Apply action to every item that satisfies test.
			-- Semantics not guaranteed if action or test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			action_exists: action /= Void
			test_exists: test /= Void
		local
			c: detachable CURSOR
			cs: detachable CURSOR_STRUCTURE [G]
		do
			if attached {CURSOR_STRUCTURE [G]} Current as acs then
				cs := acs
				c := acs.cursor
			end
			from
				start
			until
				after
			loop
				if test.item ([item]) then
					action.call ([item])
				end
				forth
			end
			if cs /= Void and c /= Void then
				cs.go_to (c)
			end
		end

	for_all (test: FUNCTION [G, BOOLEAN]): BOOLEAN
			-- Is test true for all items?
			-- Semantics not guaranteed if test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exists: test /= Void
		local
			c: detachable CURSOR
			cs: detachable CURSOR_STRUCTURE [G]
		do
			if attached {CURSOR_STRUCTURE [G]} Current as acs then
				cs := acs
				c := acs.cursor
			end
			from
				start
				Result := True
			until
				after or not Result
			loop
				Result := test.item ([item])
				forth
			end
			if cs /= Void and c /= Void then
				cs.go_to (c)
			end
		ensure then -- from LINEAR
			empty: is_empty implies Result
		end

	new_cursor: ITERATION_CURSOR [G]
			-- Fresh cursor associated with current structure
		do
			if attached tree as t then
				Result := t.new_cursor
			else
				create {EMPTY_ITERATION_CURSOR [G]} Result
			end
		ensure -- from ITERABLE
			result_attached: Result /= Void
		end

	there_exists (test: FUNCTION [G, BOOLEAN]): BOOLEAN
			-- Is test true for at least one item?
			-- Semantics not guaranteed if test changes the structure;
			-- in such a case, apply iterator to clone of structure instead.
			-- (from LINEAR)
		require -- from TRAVERSABLE
			test_exists: test /= Void
		local
			c: detachable CURSOR
			cs: detachable CURSOR_STRUCTURE [G]
		do
			if attached {CURSOR_STRUCTURE [G]} Current as acs then
				cs := acs
				c := acs.cursor
			end
			from
				start
			until
				after or Result
			loop
				Result := test.item ([item])
				forth
			end
			if cs /= Void and c /= Void then
				cs.go_to (c)
			end
		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
	comparison_mode_equal: attached tree as t implies object_comparison = t.object_comparison

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

		-- from COMPARABLE_STRUCT
	empty_constraint: min_max_available implies not is_empty

		-- from BILINEAR
	not_both: not (after and before)
	before_constraint: before implies off

		-- from LINEAR
	after_constraint: after implies off

		-- from TRAVERSABLE
	empty_constraint: is_empty implies off

		-- from TRAVERSABLE_SUBSET
	empty_definition: is_empty = (count = 0)
	count_range: count >= 0

note
	copyright: "Copyright (c) 1984-2019, 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 BINARY_SEARCH_TREE_SET

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