redef fun convert(str) do return str

	redef fun convert(str)
	do
		var id = values.index_of(str)
		if id == -1 then
			var e = "Unrecognized value for option {names.join(", ")}.\n"
			e += "Expected values are: {values.join(", ")}."
			errors.add(e)
		end
		return id
	end

	redef fun convert(str)
	do
		if str.is_int then return str.to_i

		errors.add "Expected an integer for option {names.join(", ")}."
		return 0
	end

	redef fun convert(str) do return str.to_f

	redef fun convert(str)
	do
		values.add(str)
		return values
	end

	redef fun convert(str)
	do
		var words = str.split(":")
		if words.length == 1 then
			return new UserGroup(str, null)
		else if words.length == 2 then
			return new UserGroup(words[0], words[1])
		else
			errors.add("Option {names.join(", ")} expected parameter in the format \"user:group\" or simply \"user\".\n")
			return null
		end
	end