    indexing
    	description: "[
    		Subsets that are traversable linearly without commitment to a concrete
    		implementation.
    	]"
    	legal: "See notice at end of class."
    	status: "See notice at end of class."
    	names: linear_subset, subset, set
    	access: membership
    	contents: generic
    	date: "$Date: 2006-01-22 18:25:44 -0800 (Sun, 22 Jan 2006) $"
    	revision: "$Revision: 56675 $"

    deferred class interface
    	LINEAR_SUBSET [G]

    feature -- Access

    	generating_type: STRING_8
    			-- Name of current object's generating type
    			-- (type of which it is a direct instance)
    			-- (from ANY)

    	generator: STRING_8
    			-- Name of current object's generating class
    			-- (base class of the type of which it is a direct instance)
    			-- (from ANY)

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

    	index: INTEGER_32
    			-- Current index

    	item: G
    			-- Current item
    			-- (from TRAVERSABLE_SUBSET)
    		require -- from TRAVERSABLE_SUBSET
    			not_off: not off

    feature -- Measurement

    	count: INTEGER_32
    			-- Number of items
    			-- (from TRAVERSABLE_SUBSET)

    feature -- Comparison

    	frozen deep_equal (some: ANY; other: like arg #1): BOOLEAN
    			-- Are `some' and `other' either both void
    			-- or attached to isomorphic object structures?
    			-- (from ANY)
    		ensure -- from ANY
    			shallow_implies_deep: standard_equal (some, other) implies Result
    			both_or_none_void: (some = Void) implies (Result = (other = Void))
    			same_type: (Result and (some /= Void)) implies some.same_type (other)
    			symmetric: Result implies deep_equal (other, some)

    	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

    	frozen equal (some: ANY; other: like arg #1): BOOLEAN
    			-- Are `some' and `other' either both void or attached
    			-- to objects considered equal?
    			-- (from ANY)
    		ensure -- from ANY
    			definition: Result = (some = Void and other = Void) or else ((some /= Void and other /= Void) and then some.is_equal (other))

    	is_equal (other: like Current): 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.is_equal (Current)
    			consistent: standard_is_equal (other) implies Result

    	is_subset (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

    	is_superset (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

    	frozen standard_equal (some: ANY; other: like arg #1): BOOLEAN
    			-- Are `some' and `other' 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
    			definition: Result = (some = Void and other = Void) or else ((some /= Void and other /= Void) and then some.standard_is_equal (other))

    	frozen standard_is_equal (other: like Current): 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
    			-- Is cursor behind last item?
    			-- (from TRAVERSABLE_SUBSET)

    	before: BOOLEAN
    			-- Is cursor at left from first item?

    	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

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

    	is_empty: BOOLEAN
    			-- Is container empty?
    			-- (from TRAVERSABLE_SUBSET)

    	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)

    	islast: BOOLEAN
    			-- Is cursor at last item?

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

    	off: BOOLEAN
    			-- Is cursor off the active items?
    			-- (from TRAVERSABLE_SUBSET)

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

    	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))

    	valid_index (n: INTEGER_32): BOOLEAN
    			-- Is `n' a valid index?
    		ensure
    			index_valid: 0 <= n and n <= count + 1

    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
    		ensure -- from CONTAINER
    			object_comparison

    	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
    		ensure -- from CONTAINER
    			reference_comparison: not object_comparison

    feature -- Cursor movement

    	forth
    			-- Move cursor to next element.
    			-- (from TRAVERSABLE_SUBSET)
    		require -- from TRAVERSABLE_SUBSET
    			not_after: not after

    	go_i_th (i: INTEGER_32)
    			-- Move cursor to `i'-th item.
    		require
    			valid_index: valid_index (i)
    		ensure
    			cursor_moved: index = i

    	start
    			-- Move cursor to first item.
    			-- (from TRAVERSABLE_SUBSET)

    feature -- Element change

    	extend (v: G)
    			-- Ensure that set includes `v'.
    			-- Was declared in SET as synonym of put.
    			-- (from SET)
    		require -- from COLLECTION
    			extendible: extendible
    		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)

    	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

    	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

    	move_item (v: G)
    			-- Move `v' to the left of cursor.
    		require
    			item_exists: v /= Void
    			item_in_set: has (v)

    	put (v: G)
    			-- Ensure that set includes `v'.
    			-- Was declared in SET as synonym of extend.
    			-- (from SET)
    		require -- from COLLECTION
    			extendible: extendible
    		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)

    	put_left (v: G)
    			-- Insert `v' before the cursor.
    		require
    			item_exists: v /= Void
    			not_before: not before
    		ensure
    			cursor_position_unchanged: index = old index + 1

    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
    		ensure then -- from SET
    			only_on_empty: Result = is_empty

    	prune (v: G)
    			-- Remove `v' if present.
    			-- (from SET)
    		require -- from COLLECTION
    			prunable: prunable
    		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)

    	prune_all (v: G)
    			-- Remove all occurrences of `v'.
    			-- (Reference or object equality,
    			-- based on object_comparison.)
    			-- (from COLLECTION)
    		require -- from COLLECTION
    			prunable: prunable
    		ensure -- from COLLECTION
    			no_more_occurrences: not has (v)

    	remove
    			-- Remove current item.
    			-- (from TRAVERSABLE_SUBSET)
    		require -- from TRAVERSABLE_SUBSET
    			not_off: not off

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

    feature -- Conversion

    	linear_representation: LINEAR [G]
    			-- Representation as a linear structure
    			-- (from CONTAINER)

    feature -- Duplication

    	copy (other: like Current)
    			-- 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: is_equal (other)

    	frozen deep_copy (other: like Current)
    			-- 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: like Current
    			-- New object structure recursively duplicated from Current.
    			-- (from ANY)
    		ensure -- from ANY
    			deep_equal: deep_equal (Current, Result)

    	duplicate (n: INTEGER_32): like Current
    			-- New structure containing min (`n', count)
    			-- items from current structure
    			-- (from SUBSET)
    		require -- from SUBSET
    			non_negative: n >= 0
    		ensure -- from SUBSET
    			correct_count_1: n <= count implies Result.count = n
    			correct_count_2: n >= count implies Result.count = count

    	frozen standard_copy (other: like Current)
    			-- 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: like Current
    			-- 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: like Current
    			-- New object equal to `Current'
    			-- twin calls copy; to change copying/twining semantics, redefine copy.
    			-- (from ANY)
    		ensure -- from ANY
    			twin_not_void: Result /= Void
    			is_equal: Result.is_equal (Current)

    feature -- Basic operations

    	frozen default: like Current
    			-- 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)

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

    	frozen do_nothing
    			-- Execute a null action.
    			-- (from ANY)

    	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
    		ensure -- from SUBSET
    			is_subset_other: is_subset (other)

    	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
    		ensure -- from SUBSET
    			is_disjoint: disjoint (other)

    	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

    feature -- Output

    	io: STD_FILES
    			-- Handle to standard file setup
    			-- (from ANY)

    	out: STRING_8
    			-- New string containing terse printable representation
    			-- of current object
    			-- Was declared in ANY as synonym of tagged_out.
    			-- (from ANY)

    	print (some: ANY)
    			-- Write terse external representation of `some'
    			-- on standard output.
    			-- (from ANY)

    	frozen tagged_out: STRING_8
    			-- New string containing terse printable representation
    			-- of current object
    			-- Was declared in ANY as synonym of out.
    			-- (from ANY)

    feature -- Platform

    	operating_environment: OPERATING_ENVIRONMENT
    			-- Objects available from the operating system
    			-- (from ANY)

    invariant
    	before_definition: before = (index = 0)

    		-- from TRAVERSABLE_SUBSET
    	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."
    	copyright: "Copyright (c) 1984-2006, Eiffel Software and others"
    	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
    	source: "[
    		Eiffel Software
    		356 Storke Road, 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 LINEAR_SUBSET