Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!uupsi!kepler1!fcaggian
From: fcaggian@kepler.com (Frank Caggiano)
Newsgroups: comp.lang.eiffel
Subject: Assertions and deferred routines
Message-ID: <443@kepler1.kepler.com>
Date: 17 Oct 90 18:46:06 GMT
Organization: Kepler Financial Mgmt., Setuket, NY
Lines: 116


According to both 'Eiffel: The language' and 'Object-oriented
Software Costruction'  pre and post conditions from deferred 
routines should be in force in any descendants.  I take this
to mean that if a deferred routine has a `require' statement
then the conditions in the statement are enforced in the 
descendents WITHOUT having to explicitly re-write the 
statements.

Is this in fact true?  I still am running 2.2 B (waiting quietly
for 2.3 ) and it appears not to be the case.

Does anyone know if this is a know bug, am I misreading the 
book or am I doing something wrong.  and if it is a bug is
it fixed in 2.3 (and when will 2.3 be released).

Here is an example of the code:
--------------------------------------------------------------------------
--  Copyright (C) Kepler Financial Mgmt.				--
--  100 North Country Rd., Setauket NY, 11733				--
--									--
-- Frank Caggiano							--
-- Thu Oct 11 10:54:20 EDT 1990						--
--------------------------------------------------------------------------
--
-- General notion of displaying a figure in  X
--
deferred class XDISPLAY_FUNCTION export
	
	display, erase

feature

	display (fig_ref: GEN_FIGURE; w: WINDOW) is
			-- Display figure in window
		require
			have_figure: not fig_ref.void;
			window_exists: not w.void;
		deferred
		end; -- display


	erase (fig_ref: GEN_FIGURE; w: WINDOW) is
			-- Erase figure from window
		require
			have_figure: not fig_ref.void;
			window_exists: not w.void;
		deferred
		end; -- erase

end; -- class XDISPLAY_FUNCTION

In this class the assertion check does not happen unless I explicitly
write out the require statement in the routine definantion.


--------------------------------------------------------------------------
--  Copyright (C) Kepler Financial Mgmt.				--
--  100 North Country Rd., Setauket NY, 11733				--
--									--
-- Frank Caggiano							--
-- Thu Oct 11 10:54:20 EDT 1990						--
--------------------------------------------------------------------------
--
--  class to draw an ellipse in X
--
class X_DRAW_ELLIPSE export
		
	display, erase

inherit

	XDISPLAY_FUNCTION
		define
			display,erase
feature

	display (fig_ref: ELLIPSE; w: GRAPH_WINDOW) is
		external
			ellipse_draw language "C"
		do
			fig_ref.xgc.set_gc;

			ellipse_draw(w.imp_reference, fig_ref.xgc.imp_ref,
					fig_ref.origin.winx(w), fig_ref.origin.winy(w),
					(fig_ref.int_major_axis * w.draw_num) div w.draw_denom,
					(fig_ref.int_minor_axis * w.draw_num) div w.draw_denom);
				
		end;

	erase (fig_ref: ELLIPSE; w: GRAPH_WINDOW) is
		-- Erase ellipse from 'w'. 
		-- NOTE: this is NOT a 'rubberband' type of erase. 
		-- See class RUBBER and its desendents. 
		external 
			ellipse_draw language "C" 
		local
			gc: GRAPHIC_IMP
		do 
			gc.create;
			gc.set_background_by_pixel(w.back_color);
			gc.set_foreground_by_pixel(w.back_color);
			gc.set_gc;

			ellipse_draw(w.imp_reference, gc.imp_ref,
					fig_ref.origin.winx(w), fig_ref.origin.winy(w),
					(fig_ref.int_major_axis * w.draw_num) div w.draw_denom,
					(fig_ref.int_minor_axis * w.draw_num) div w.draw_denom);

		end; -- erase
end;
-- 
Frank Caggiano                      INTERNET: fcaggian@kepler.com  
Kepler Financial Management, Ltd.       UUCP: ..!uunet!kepler1!fcaggian
100 North Country Rd.                    fax: (516) 751-8678
Sekauket, NY 11733                     voice: (516) 689-6300