note
	description: "Collection, where each element must be unique."
	library: "Free implementation of ELKS library"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	names: set
	access: membership
	contents: generic
	date: "$Date: 2019-07-05 15:26:16 +0000 (Fri, 05 Jul 2019) $"
	revision: "$Revision: 103325 $"

deferred class 
	SET [G]

inherit
	COLLECTION [G]
		rename
			has as has alias "∋"
		redefine
			changeable_comparison_criterion
		end

feature -- Measurement

	count: INTEGER_32
			-- Number of items
		deferred
		end
	
feature -- Element change

	extend (v: G)
			-- Ensure that set includes v.
			-- Was declared in SET as synonym of put.
		deferred
		ensure then
			in_set_already: old has (v) implies (count = old count)
			added_to_set: not old has (v) implies (count = old count + 1)
		end

	put (v: G)
			-- Ensure that set includes v.
			-- Was declared in SET as synonym of extend.
		deferred
		ensure then
			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

	prune (v: G)
			-- Remove v if present.
		deferred
		ensure then
			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

	changeable_comparison_criterion: BOOLEAN
			-- May object_comparison be changed?
			-- (Answer: only if set empty; otherwise insertions might
			-- introduce duplicates, destroying the set property.)
		do
			Result := is_empty
		ensure then
			only_on_empty: Result = is_empty
		end
	
note
	copyright: "Copyright (c) 1984-2019, 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 SET

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