indexing
	description: "Structures that can be dynamically modified"
	library: "Gobo Eiffel Structure Library"
	author: "Eric Bezault <ericb@gobo.demon.co.uk>"
	copyright: "Copyright (c) 1997, Eric Bezault"

deferred class interface
	DS_DYNAMIC [G]

feature -- Access

	first: G
			-- Item in structure
			-- (from DS_EXTENDIBLE)
		require -- from DS_LINEAR
			not_empty: not is_empty
		require -- from DS_EXTENDIBLE
			not_empty: not is_empty
		require -- from DS_EXTENDIBLE
			not_empty: not is_empty
		ensure -- from DS_LINEAR
			has_first: has (Result)

	last: G
			-- Last item in structure
			-- (from DS_BILINEAR)
		require -- from DS_BILINEAR
			not_empty: not is_empty
		ensure -- from DS_BILINEAR
			has_last: has (Result)

	new_cursor: DS_BILINEAR_CURSOR [G]
			-- New cursor for traversal
			-- (from DS_BILINEAR)
		ensure -- from DS_TRAVERSABLE
			cursor_not_void: Result /= void;
			valid_cursor: valid_cursor (Result)

	searcher: DS_BILINEAR_SEARCHER [G]
			-- Structure searcher
			-- (from DS_BILINEAR)
	
feature -- Measurement

	count: INTEGER
			-- Number of items in structure
			-- (from DS_CONTAINER)

	occurrences (v: G): INTEGER
			-- Number of times v appears in structure
			-- (Use searcher's comparison criterion.)
			-- (from DS_SEARCHABLE)
		ensure -- from DS_SEARCHABLE
			positive: Result >= 0;
			has: has (v) implies Result >= 1
	
feature -- Comparison

	is_equal (other: like Current): BOOLEAN
			-- Is current structure equal to other?
			-- (from DS_CONTAINER)
		require -- from GENERAL
			other_not_void: other /= void
		ensure -- from GENERAL
			symmetric: Result implies other.is_equal (Current);
			consistent: standard_is_equal (other) implies Result
		ensure then -- from DS_CONTAINER
			same_count: Result implies count = other.count
		ensure then -- from DS_CONTAINER
			same_count: Result implies count = other.count
	
feature -- Status report

	extendible (n: INTEGER): BOOLEAN
			-- May structure be extended with n items?
			-- (from DS_EXTENDIBLE)
		require -- from DS_EXTENDIBLE
			positive_n: n >= 0

	has (v: G): BOOLEAN
			-- Does structure incluse v?
			-- (Use searcher's comparison criterion.)
			-- (from DS_SEARCHABLE)
		ensure -- from DS_SEARCHABLE
			not_empty: Result implies not is_empty

	is_empty: BOOLEAN
			-- Is structure empty?
			-- (from DS_CONTAINER)

	valid_cursor (a_cursor: like new_cursor): BOOLEAN
			-- Is a_cursor a valid cursor?
			-- (A cursor might become invalid if structure
			-- has been modified during traversal.)
			-- (from DS_TRAVERSABLE)
		require -- from DS_TRAVERSABLE
			a_cursor_not_void: a_cursor /= void
		ensure -- from DS_TRAVERSABLE
			is_valid: Result implies a_cursor.is_valid
	
feature -- Element change

	append_first (other: DS_LINEAR [G])
			-- Add items of other to structure.
			-- (from DS_EXTENDIBLE)
		require -- from DS_EXTENDIBLE
			other_not_void: other /= void
		ensure -- from DS_EXTENDIBLE
			new_count: count = old count + other.count

	append_last (other: DS_LINEAR [G])
			-- Add items of other to end of structure.
		require
			other_not_void: other /= void
		ensure
			new_count: count = old count + other.count

	append_left (other: DS_LINEAR [G]; a_cursor: like new_cursor)
			-- Add items of other to left of a_cursor position.
		require
			other_not_void: other /= void;
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_before: not a_cursor.before
		ensure
			new_count: count = old count + other.count

	append_right (other: DS_LINEAR [G]; a_cursor: like new_cursor)
			-- Add items of other to right of a_cursor position.
		require
			other_not_void: other /= void;
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_after: not a_cursor.after
		ensure
			new_count: count = old count + other.count

	extend_first (other: DS_LINEAR [G])
			-- Add items of other to structure.
			-- (from DS_EXTENDIBLE)
		require -- from DS_EXTENDIBLE
			other_not_void: other /= void;
			extendible: extendible (other.count)
		ensure -- from DS_EXTENDIBLE
			new_count: count = old count + other.count

	extend_last (other: DS_LINEAR [G])
			-- Add items of other to end of structure.
		require
			other_not_void: other /= void;
			extendible: extendible (other.count)
		ensure
			new_count: count = old count + other.count

	extend_left (other: DS_LINEAR [G]; a_cursor: like new_cursor)
			-- Add items of other to left of a_cursor position.
		require
			other_not_void: other /= void;
			extendible: extendible (other.count);
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_before: not a_cursor.before
		ensure
			new_count: count = old count + other.count

	extend_right (other: DS_LINEAR [G]; a_cursor: like new_cursor)
			-- Add items of other to right of a_cursor position.
		require
			other_not_void: other /= void;
			extendible: extendible (other.count);
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_after: not a_cursor.after
		ensure
			new_count: count = old count + other.count

	force_first (v: G)
			-- Add v to beginning of structure.
		ensure -- from DS_EXTENDIBLE
			one_more: count = old count + 1
		ensure then
			inserted: first = v

	force_last (v: G)
			-- Add v to end of structure.
		ensure
			one_more: count = old count + 1;
			inserted: last = v

	force_left (v: G; a_cursor: like new_cursor)
			-- Add v to left of a_cursor position.
		require
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_before: not a_cursor.before
		ensure
			one_more: count = old count + 1

	force_right (v: G; a_cursor: like new_cursor)
			-- Add v to right of a_cursor position.
		require
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_after: not a_cursor.after
		ensure
			one_more: count = old count + 1

	put_first (v: G)
			-- Add v to beginning of structure.
		require -- from DS_EXTENDIBLE
			extendible: extendible (1)
		ensure -- from DS_EXTENDIBLE
			one_more: count = old count + 1
		ensure then
			inserted: first = v

	put_last (v: G)
			-- Add v to end of structure.
		require
			extendible: extendible (1)
		ensure
			one_more: count = old count + 1;
			inserted: last = v

	put_left (v: G; a_cursor: like new_cursor)
			-- Add v to left of a_cursor position.
		require
			extendible: extendible (1);
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_before: not a_cursor.before
		ensure
			one_more: count = old count + 1

	put_right (v: G; a_cursor: like new_cursor)
			-- Add v to right of a_cursor position.
		require
			extendible: extendible (1);
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_after: not a_cursor.after
		ensure
			one_more: count = old count + 1
	
feature -- Removal

	delete (v: G)
			-- Remove all occurrences of v.
			-- (Use searcher's comparison criterion.)
		ensure
			deleted: not has (v)

	keep_first (n: INTEGER)
			-- Keep n items in structure.
			-- (from DS_EXTENDIBLE)
		require -- from DS_EXTENDIBLE
			valid_n: 0 <= n and n <= count
		ensure -- from DS_EXTENDIBLE
			new_count: count = n

	keep_last (n: INTEGER)
			-- Keep n last items in structure.
		require
			valid_n: 0 <= n and n <= count
		ensure
			new_count: count = n

	prune_first (n: INTEGER)
			-- Remove n items from structure.
			-- (from DS_EXTENDIBLE)
		require -- from DS_EXTENDIBLE
			valid_n: 0 <= n and n <= count
		ensure -- from DS_EXTENDIBLE
			new_count: count = old count - n

	prune_last (n: INTEGER)
			-- Remove n last items from structure.
		require
			valid_n: 0 <= n and n <= count
		ensure
			new_count: count = old count - n

	prune_left (n: INTEGER; a_cursor: like new_cursor)
			-- Remove n items to left of a_cursor position.
		require
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			valid_n: 0 <= n and n < a_cursor.index
		ensure
			new_count: count = old count - n

	prune_right (n: INTEGER; a_cursor: like new_cursor)
			-- Remove n items to right of a_cursor position.
		require
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			valid_n: 0 <= n and n <= count - a_cursor.index
		ensure
			new_count: count = old count - n

	remove_first
			-- Remove an item from structure.
			-- (from DS_EXTENDIBLE)
		require -- from DS_EXTENDIBLE
			not_empty: not is_empty
		ensure -- from DS_EXTENDIBLE
			one_less: count = old count - 1

	remove_at (a_cursor: like new_cursor)
			-- Remove item at a_cursor position.
			-- Move a_cursor to next position.
		require
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_off: not a_cursor.off
		ensure
			one_less: count = old count - 1

	remove_last
			-- Remove last item from structure.
		require
			not_empty: not is_empty
		ensure
			one_less: count = old count - 1

	remove_left (a_cursor: like new_cursor)
			-- Remove item to left of a_cursor position.
		require
			not_empty: not is_empty;
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_before: not a_cursor.before;
			not_first: not a_cursor.is_first
		ensure
			one_less: count = old count - 1

	remove_right (a_cursor: like new_cursor)
			-- Remove item to right of a_cursor position.
		require
			not_empty: not is_empty;
			cursor_not_void: a_cursor /= void;
			valid_cursor: valid_cursor (a_cursor);
			not_before: not a_cursor.after;
			not_first: not a_cursor.is_last
		ensure
			one_less: count = old count - 1

	wipe_out
			-- Remove all items from structure.
			-- (from DS_CONTAINER)
		ensure -- from DS_CONTAINER
			wipe_out: is_empty
		ensure -- from DS_CONTAINER
			wipe_out: is_empty
	
feature -- Setting

	set_searcher (a_searcher: like searcher)
			-- Set searcher to a_searcher.
			-- (from DS_SEARCHABLE)
		require -- from DS_SEARCHABLE
			a_searcher_not_void: a_searcher /= void
		ensure -- from DS_SEARCHABLE
			searcher_set: searcher = a_searcher
	
invariant

		-- from GENERAL
	reflexive_equality: standard_is_equal (Current);
	reflexive_conformance: conforms_to (Current);
		-- from DS_CONTAINER
	positive_count: count >= 0;
	empty_definition: is_empty = (count = 0);
		-- from DS_SEARCHABLE
	searcher_not_void: searcher /= void;

end -- class DS_DYNAMIC