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	description: "[
		Active structures, which always have a current position
		accessible through a cursor.
	]"
	status: "See notice at end of class"
	names: cursor_structure, access
	access: cursor, membership
	contents: generic
	date: "$Date: 2001-11-16 20:32:23 +0000 (Fri, 16 Nov 2001) $"
	revision: "$Revision: 51435 $"

deferred class 
	CURSOR_STRUCTURE [G]

feature -- Access

	cursor: CURSOR is
			-- Current cursor position
		deferred
		end

	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
			-- (from ACTIVE)
		require -- from ACTIVE
			readable: readable
		deferred
		end
	
feature -- Measurement

	occurrences (v: G): INTEGER is
			-- Number of times v appears in structure
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from BAG)
		deferred
		ensure -- from BAG
			non_negative_occurrences: Result >= 0
		end
	
feature -- Status report

	changeable_comparison_criterion: BOOLEAN is
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)
		do
			Result := True
		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	empty: BOOLEAN is
		obsolete "ELKS 2000: Use `is_empty' instead"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 there no element?
			-- (from CONTAINER)
		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)

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

	readable: BOOLEAN is
			-- Is there a current item that may be read?
			-- (from ACTIVE)
		deferred
		end

	valid_cursor (p: CURSOR): BOOLEAN is
			-- Can the cursor be moved to position p?
		deferred
		end

	writable: BOOLEAN is
			-- Is there a current item that may be modified?
			-- (from ACTIVE)
		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

	go_to (p: CURSOR) is
			-- Move cursor to position p.
		require
			cursor_position_valid: valid_cursor (p)
		deferred
		end
	
feature -- Element change

	extend (v: G) is
			-- Add a new occurrence of v.
			-- (from BAG)
		require -- from COLLECTION
			extendible: extendible
		deferred
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		ensure then -- from BAG
			one_more_occurrence: occurrences (v) = old (occurrences (v)) + 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

	put (v: G) is
			-- Ensure that structure includes v.
			-- Was declared in COLLECTION as synonym of extend.
			-- (from COLLECTION)
		require -- from COLLECTION
			extendible: extendible
		deferred
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		end

	replace (v: G) is
			-- Replace current item by v.
			-- (from ACTIVE)
		require -- from ACTIVE
			writable: writable
		deferred
		ensure -- from ACTIVE
			item_replaced: item = v
		end
	
feature -- Removal

	prune (v: G) is
			-- Remove one occurrence of v if any.
			-- (Reference or object equality,
			-- based on object_comparison.)
			-- (from COLLECTION)
		require -- from COLLECTION
			prunable: prunable
		deferred
		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.
			-- (from ACTIVE)
		require -- from ACTIVE
			prunable: prunable
			writable: writable
		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
	
invariant

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)
		-- from ACTIVE
	writable_constraint: writable implies readable
	empty_constraint: is_empty implies (not readable) and (not writable)

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 CURSOR_STRUCTURE


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