🚀 go-pugleaf

In article <254@eiffel.UUCP> bertrand@eiffel.UUCP (Bertrand Meyer) writes:
>From <1799@novavax.UUCP> by weiner@novavax.UUCP (Bob Weiner):
>
>> Rather than sprinkle pre- and post-conditions around routines that say:
>> 
>>     require
>>        param > 0
>> 
>> and other such things, it makes sense to create classes for POS_INT,
>> NON_NEG_INT and so forth and then type the formal parameters of the
>> routines.
...
>    In all these cases we will have to resort to assertions anyway.
...

It's really a case of where we have to assert. Surely much better in a class
than in each of its uses since the constraint is a property of the class.

Perhaps, for efficiency's sake, it would be acceptable to dissallow
multiple inheritance and feature (re)defintion for descendants of
basic types. Thus:

   class INTERVAL_1_10 export
      repeat INTEGER	
   inherit
      INTEGER
   invariant
      Current >= 1 and Current <= 10;
   end

Sure, this restricts us to static interval bounds, but then this is
all most programming languages provide. And it's better than what we
have now.

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inherit STD_DISCLAIMER;
                     
    Steve Tynor
    Georgia Tech Research Institute
    Artificial Intelligence Branch
    tynor@prism.gatech.edu