deferred class interface BASIC_PEN feature(s) from BASIC_PEN -- Colour set_color (cl: COLOR) -- Set pen colour. require valid_color: cl /= Void ensure keep_reference: color = cl feature(s) from BASIC_PEN -- Line style set_line_solid -- Set line style: solid (default). set_line_solid_inside_frame -- Set line style: solid, kept inside rectangles. set_line_invisible -- Set line style: no line (invisible). set_line_dash -- Set line style: - - - - set_line_dot -- Set line style: ....... set_line_dash_dot -- Set line style: -.-.-.- set_line_dash_dot_dot -- Set line style: -..-..- invariant valid_color: color /= Void; end of deferred BASIC_PEN