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From: jans@mako.UUCP (Jan Steinman)
Newsgroups: net.lang
Subject: Re: levelheight: automatic "nil pointer" handling
Message-ID: <536@mako.UUCP>
Date: Thu, 24-Jan-85 13:01:44 EST
Article-I.D.: mako.536
Posted: Thu Jan 24 13:01:44 1985
Date-Received: Fri, 25-Jan-85 21:56:47 EST
References: <2340@hplabsc.UUCP> <4948@utzoo.UUCP> <6292@boring.UUCP>
Reply-To: jans@mako.UUCP (Jan Steinman)
Distribution: net
Organization: Tektronix, Wilsonville OR
Lines: 30

In article <6292@boring.UUCP> steven@boring.UUCP (Steven Pemberton) writes:
>I believe that programming languages can go much further in the help they
>give programmers than they do at present. For instance, it is possible to
>statically guarantee that nil pointers are never dereferenced (imagine the
>bugs that that would prevent!) but I know of no language that supports it.

Ada supports this:

|Not only can we explicitly create objects designated by access values, but we
|can also destroy them.  Such objects will no longer be accessible if all
|references to them are removed, such as:
|
|	MY_PACKET := new BUFFER;	-- a BUFFER object is created
|	MY_PACKET := null;		-- the original object is unreachable
|
|Furthermore, these dynamic objects will be destroyed once we leave the scope
|of the access objects.  For example:
|
|	declare
|		POINTER : BUFFER_POINTER;
|	begin
|		...
|		POINTER := new BUFFER;	-- create a BUFFER object
|		...
|	end;				-- BUFFER object is destroyed

From "Software Engineering With Ada", Grady Booch, p.105.
-- 
:::::: Jan Steinman		Box 1000, MS 61-161	(w)503/685-2843 ::::::
:::::: tektronix!tekecs!jans	Wilsonville, OR 97070	(h)503/657-7703 ::::::