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Date: 17 Dec 92 01:31:21 GMT
From: eachus@mitre-bedford.arpa  (Robert I. Eachus)
Subject: Re: Language pitfalls (was Re: FORTRAN bug)
Message-ID: <EACHUS.92Dec16203121@oddjob.mitre.org>
List-Id: <comp.lang.ada>

In article <256@visicom.com> rlk@VisiCom.COM (Bob Kitzberger) writes:

   Robert, I can't think of a reason to have a function that does nothing
   but raise an exception... can you provide an example?  (I'm not
   questioning the need for it -- just curious)

   Stubbing is the major reason for doing this, i.e. something not
available in the current version of the software, but the interface is
provided.

   Another case is where a generic requires an operation as a formal
parameter which is meaningless for a particular actual.  There are
cases where providing a function which raises an error is more useful
than rewriting the generic.  For example, assume you have a "standard"
interface to IO devices, for some current_position would return a
value, for other devices the function of the same name would
immediately raise an exception.

   A more subtle use in when you are not sure an obsolete interface
or object can be eliminated.  Putting in a function which prints a
meaningful message then returns is more polite than ripping it out,
and waiting until some user of the package screams.

   One more use I have found was for a private type where user created
objects were verboten.  (Put in a component with such a function as
the default initial value.  User created objects will cause the
function to be evaluated.)

   Lots of uses, but only the difficulties the rule creates in
stubbers is compelling.

--

					Robert I. Eachus

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