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Subject: Re: Structured exception information
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Date: 2007-01-19T18:57:46+00:00
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Dmitry A. Kazakov wrote:
> 
> OK, what about an alternative. Let's forget about preconditions, let's call
> it *constraint*. This is what Ada has since its beginning. What about
> allowing more generous constraint expressions put on the subtypes? It could
> have the desired effect, IMO. The "precondition" could be a constraint on
> the subtype of an in-parameter. The "postcondition" could be one on the
> subtype of an out-parameter. We could allow ad-hoc subtypes in subprogram
> signatures, for lazy guys...

This is a good point. Ada's subtypes have always been a form of dynamic 
precondition. I've always thought it better to write

Length : in Natural

than

Length : in Integer

--#pre Length >= 0

So it would be nice if this concept could be extended to essentially 
handle dynamic preconditions. Any suggestions how to apply this to, say

(DS : in out Data_Structure; Index : in Positive)

--#pre Index in 1 .. Size (DS);

?