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From: Matthew J Heaney <mheaney@on2.com>
Subject: Re: Design by Contract (was Re: Interesting thread in
 comp.lang.eiffel)
Date: 2000/07/12
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Newsgroups: comp.lang.eiffel,comp.lang.ada
Date: 2000-07-12T00:00:00+00:00
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Greg <gmc333NOgmSPAM@my-deja.com.invalid> writes:

> In Eiffel, DbC works with inheritance. So a subclass is bound to the
> same contract as its parent class automatically. Not being an Ada
> guru, I'd guess you would have to copy the parent's contract into the
> child, leading to undesirable duplication.

Yes, it's true that Eiffel's contract-checking is more sophisticated
than a simple assertion-check.  However, Eiffel *has* to be this way,
because the idiom in that language is inheritance-based programming.
Abstractions are composed using inheritance.

But in Ada, it's very rare that you have deep inheritance lattices,
because there are language features that allow you to compose
abstractions using aggregation.  So contract checks don't need to be any
more sophisticated than simple assertion checks.