Re: Typing in Ada

[Marin David Condic <nobody@noplace.com>]

Sometimes its an issue for verification. High reliability systems often 
prohibit the inclusion of any code that is not necessary to meet a 
requirement because it presents an opportunity to introduce an error 
that would not need to occur because there is no requirement to do this. 
So a similar argument can be made for restricting the number of apples 
even if the spec doesn't say Thou Shalt Not Count 101 Apples. Kind of a 
case of avoiding building the proverbial brick outhouse - don't make it 
do anything more than is required because you can't then be sure it will 
handle those cases correctly.

But then again, there are few of those sort of systems and far many more 
of the type where this would not be an issue. Then saying "At minimum, 
100 apples must be supported..." is fine and if the programmer gives you 
2**32 apples, it probably doesn't hurt anything.

MDC


Wes Groleau wrote:
> 
> In a way, you are correct.  But why must we put
> so much effort into preventing behavior that is
> not prohibited just because it is not required?
> 
> Does the specification say ... ?
>   "The program shall not tolerate apple counts higher than 100"
> 
> Did some domain expert persuade the programmers that 101 apples
> was not reasonable?
> 
> In other words, when a specification says
> "A count of 100 must be supported,"  the
> programmers should NOT mentally rewrite it
> to "Counts larger than 100 must not be supported."
> 


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Marin David Condic
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