note
	description: "[
		Active structures, which always have a current position
		accessible through a cursor.
	]"
	library: "Free implementation of ELKS library"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	names: cursor_structure, access
	access: cursor, membership
	contents: generic
	date: "$Date: 2012-07-23 21:02:19 +0000 (Mon, 23 Jul 2012) $"
	revision: "$Revision: 91989 $"

deferred class 
	CURSOR_STRUCTURE [G]

feature {NONE} -- Initialization

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

	cursor: CURSOR
			-- Current cursor position
		deferred
		ensure
			cursor_not_void: Result /= Void
		end

	generating_type: TYPE [detachable CURSOR_STRUCTURE [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

	has (v: G): BOOLEAN
			-- 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
			-- Current item
			-- (from ACTIVE)
		require -- from ACTIVE
			readable: readable
		deferred
		end

	new_cursor: ITERATION_CURSOR [G]
			-- Fresh cursor associated with current structure
			-- (from ITERABLE)
		deferred
		ensure -- from ITERABLE
			result_attached: Result /= Void
		end
	
feature -- Measurement

	occurrences (v: G): INTEGER_32
			-- 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 {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

	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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: yes by default.)
			-- (from CONTAINER)
		do
			Result := True
		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

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

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

	is_empty: BOOLEAN
			-- Is there no element?
			-- (from CONTAINER)
		deferred
		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)

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

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

	replaceable: BOOLEAN
			-- Can current item be replaced?
			-- (from ACTIVE)
		do
			Result := True
		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

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

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

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

	extend (v: G)
			-- Add a new occurrence of v.
			-- (from BAG)
		require -- from COLLECTION
			extendible: extendible
		deferred
		ensure -- from COLLECTION
			item_inserted: is_inserted (v)
		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

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

	prune (v: G)
			-- 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)
			-- 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.
			-- (from ACTIVE)
		require -- from ACTIVE
			prunable: prunable
			writable: writable
		deferred
		end

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

	linear_representation: LINEAR [G]
			-- Representation as a linear structure
			-- (from CONTAINER)
		deferred
		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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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: CURSOR_STRUCTURE [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 CURSOR_STRUCTURE [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 CURSOR_STRUCTURE [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 ACTIVE
	writable_constraint: writable implies readable
	empty_constraint: is_empty implies (not readable) and (not writable)

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

note
	copyright: "Copyright (c) 1984-2012, 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 CURSOR_STRUCTURE

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