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	description: "Subsets that are traversable sequentially"
	status: "See notice at end of class"
	names: traversable_subset, set, subset
	access: sequential
	contents: generic
	date: "$Date: 2001-11-16 20:32:23 +0000 (Fri, 16 Nov 2001) $"
	revision: "$Revision: 51435 $"

deferred class 
	TRAVERSABLE_SUBSET [G]

feature -- Access

	has (v: G): BOOLEAN is
			-- Does structure include v?
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from CONTAINER)
		deferred
		ensure -- from CONTAINER
			not_found_in_empty: Result implies not is_empty
		end

	item: G is
			-- Current item
		require
			not_off: not off
		deferred
		end
	
feature -- Measurement

	count: INTEGER is
			-- Number of items
		deferred
		end
	
feature -- Comparison

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

	is_subset (other: TRAVERSABLE_SUBSET [G]): BOOLEAN is
			-- Is current set a subset of other?
		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.has (item)
				loop
					forth
				end
				if off then
					Result := True
				end
			elseif is_empty then
				Result := True
			end
		end

	is_superset (other: SUBSET [G]): BOOLEAN is
			-- 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.is_subset (Current)
		end
	
feature -- Status report

	after: BOOLEAN is
			-- Is cursor behind last item?
		deferred
		end

	empty: BOOLEAN is
		obsolete "ELKS 2000: Use `is_empty' instead"
			-- Is there no element?
			-- (from CONTAINER)
		do
			Result := is_empty
		end

	extendible: BOOLEAN is
			-- May new items be added?
			-- (from COLLECTION)
		deferred
		end

	is_empty: BOOLEAN is
			-- Is container empty?
		deferred
		end

	is_inserted (v: G): BOOLEAN is
			-- 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
			-- Is cursor off the active items?
		deferred
		end

	prunable: BOOLEAN is
			-- May items be removed?
			-- (from COLLECTION)
		deferred
		end
	
feature -- Status setting

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

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

	forth is
			-- Move cursor to next element.
		require
			not_after: not after
		deferred
		end

	start is
			-- Move cursor to first item.
		deferred
		end
	
feature -- Element change

	extend (v: G) is
			-- Ensure that set includes v.
			-- Was declared in SET as synonym of put.
			-- (from SET)
		require -- from COLLECTION
			extendible: extendible
		deferred
		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]) is
			-- 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
		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]) is
			-- Add all items of other.
		require -- from SUBSET
			set_exists: other /= void
			same_rule: object_comparison = other.object_comparison
		local
			lin_rep: LINEAR [G]
		do
			lin_rep ?= other
			if lin_rep = void then
				lin_rep := other.linear_representation
			end
			from
				lin_rep.start
			until
				lin_rep.off
			loop
				extend (lin_rep.item)
				lin_rep.forth
			end
		end

	put (v: G) is
			-- Ensure that set includes v.
			-- Was declared in SET as synonym of extend.
			-- (from SET)
		require -- from COLLECTION
			extendible: extendible
		deferred
		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 is
			-- May object_comparison be changed?
			-- (Answer: only if set empty; otherwise insertions might
			-- introduce duplicates, destroying the set property.)
			-- (from SET)
		do
			Result := is_empty
		ensure then -- from SET
			only_on_empty: Result = is_empty
		end

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

	remove is
			-- Remove current item.
		require
			not_off: not off
		deferred
		end

	wipe_out is
			-- Remove all items.
			-- (from COLLECTION)
		require -- from COLLECTION
			prunable
		deferred
		ensure -- from COLLECTION
			wiped_out: is_empty
		end
	
feature -- Conversion

	linear_representation: LINEAR [G] is
			-- Representation as a linear structure
			-- (from CONTAINER)
		deferred
		end
	
feature -- Duplication

	duplicate (n: INTEGER): like Current is
			-- New structure containing min (n, count)
			-- items from current structure
			-- (from SUBSET)
		require -- from SUBSET
			non_negative: n >= 0
		deferred
		ensure -- from SUBSET
			correct_count_1: n <= count implies Result.count = n
			correct_count_2: n >= count implies Result.count = count
		end
	
feature -- Basic operations

	intersect (other: TRAVERSABLE_SUBSET [G]) is
			-- Remove all items not in other.
			-- No effect if other is_empty.
		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.has (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]) is
			-- Remove all items also in other.
		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.has (item) then
						remove
					else
						forth
					end
				end
			end
		ensure -- from SUBSET
			is_disjoint: disjoint (other)
		end

	symdif (other: TRAVERSABLE_SUBSET [G]) is
			-- Remove all items also in other, and add all
			-- items of other not already present.
		require -- from SUBSET
			set_exists: other /= void
			same_rule: object_comparison = other.object_comparison
		local
			s: SUBSET_STRATEGY [G]
		do
			if not other.is_empty then
				if is_empty then
					copy (other)
				else
					s := subset_strategy (other)
					s.symdif (Current, other)
				end
			end
		end
	
feature {NONE} -- Implementation

	subset_strategy (other: TRAVERSABLE_SUBSET [G]): SUBSET_STRATEGY [G] is
			-- Subset strategy suitable for the type of the contained elements.
		require
			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] is
			-- Strategy to calculate several subset features selected depending
			-- on the dynamic type of v and other
		require
			item_exists: v /= void
			other_exists: other /= void
		deferred
		ensure
			strategy_set: Result /= void
		end
	
invariant

	empty_definition: is_empty = (count = 0)
	count_range: count >= 0
		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

indexing
	library: "[
			EiffelBase: Library of reusable components for Eiffel.
	]"
	status: "[
			Copyright 1986-2001 Interactive Software Engineering (ISE).
			For ISE customers the original versions are an ISE product
			covered by the ISE Eiffel license and support agreements.
	]"
	license: "[
			EiffelBase may now be used by anyone as FREE SOFTWARE to
			develop any product, public-domain or commercial, without
			payment to ISE, under the terms of the ISE Free Eiffel Library
			License (IFELL) at http://eiffel.com/products/base/license.html.
	]"
	source: "[
			Interactive Software Engineering Inc.
			ISE Building
			360 Storke Road, Goleta, CA 93117 USA
			Telephone 805-685-1006, Fax 805-685-6869
			Electronic mail <info@eiffel.com>
			Customer support http://support.eiffel.com
	]"
	info: "[
			For latest info see award-winning pages: http://eiffel.com
	]"

end -- class TRAVERSABLE_SUBSET


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