note
	description: "Value of a configuration option."
	legal: "See notice at end of class."
	status: "See notice at end of class."
	date: "$Date$"
	revision: "$Revision$"

deferred class CONF_VALUE

feature -- Status report

	is_set: BOOLEAN
			-- Is option value set?

feature -- Modification

	unset
			-- Ensure no option value is set.
		do
			is_set := False
		ensure
			not_is_set: not is_set
		end

	set_safely (other: like Current)
			-- Set option value from `other' if it is not set yet.
		require
			other_attached: other /= Void
		do
			if not is_set and then Current /~ other then
				copy (other)
				is_set := True
			end
		ensure
			old_value: (old is_set or else old twin ~ other) implies is_equal (old twin)
			new_value: (not old is_set and then old twin /~ other) implies is_set
		end

note
	copyright:	"Copyright (c) 1984-2009, Eiffel Software"
	license:	"GPL version 2 (see http://www.eiffel.com/licensing/gpl.txt)"
	licensing_options:	"http://www.eiffel.com/licensing"
	copying: "[
			This file is part of Eiffel Software's Eiffel Development Environment.
			
			Eiffel Software's Eiffel Development Environment is free
			software; you can redistribute it and/or modify it under
			the terms of the GNU General Public License as published
			by the Free Software Foundation, version 2 of the License
			(available at the URL listed under "license" above).
			
			Eiffel Software's Eiffel Development Environment is
			distributed in the hope that it will be useful, but
			WITHOUT ANY WARRANTY; without even the implied warranty
			of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
			See the GNU General Public License for more details.
			
			You should have received a copy of the GNU General Public
			License along with Eiffel Software's Eiffel Development
			Environment; if not, write to the Free Software Foundation,
			Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
		]"
	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