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From: donh@syd.csa.com.au (Don Harrison)
Subject: Re: Safety-critical development in Ada and Eiffel
Date: 1997/07/21
Message-ID: <EDnA6M.FGx@syd.csa.com.au>#1/1
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Newsgroups: comp.object,comp.software-eng,comp.lang.ada,comp.lang.eiffel
Date: 1997-07-21T00:00:00+00:00
List-Id: <comp.lang.ada>


Robert Dewar wrote:

:Don Harrison says
:
:<<Yes, I should have realised! It's the old workaround to the infuriating Ada83
:visibility problem of not being able to see the predefined operators of a user-d
:efined(?) type in client code. In spite of already with-ing the
:supplier module (which I don't think you should have to do, anyway - if you
:*use* features exported by a package, explicitly importing it is redundant),
:you can't see (hence, use) the imported operators.
:>>
:
:
:My goodness, surprising that anyone would think this, but then I guess there
:are people who really prefer uncontrolled anarchy.

No, that's what you get when you don't practise formal software engineering
where you need it. :)

However, your view is quite justified in the case of Ada which doesn't support 
well-specified, safe-to-use software components to the extent that Eiffel 
does. In view of this, you're quite justified in perceiving a need to document 
in one place all the modules used by another. In contrast, because Eiffel 
*does* support safe reuse of components, it isn't as important to separately 
document the modules used.

In any case, if you really want this in Eiffel, it's trivial to write an 
extraction tool to produce it. Implementations may already provide this.

:To me one of the real advantages in Ada is that you know right away, right
:at the start of the package, exactly what services are being used, 

See above.

:and you can more easily excercise control over this. 

This is not true unless you have a CM tool which allows you to separately
control the with-clauses of a package body and the rest of the body. I think
most will agree this would be ridiculous.

:If you let code anywwhere
:reach anywhere easily, you have a recipe for mess.

I agree for Ada. I don't agree for Eiffel which gives you a high level of 
confidence that you can reuse with impunity. Reusing certain modules may 
happen to be nonsensical but that's a design issue - not a reuse issue - and 
irrelevant to this argument.

:The requirement to write a with clause is also the requirement to think
:about whether it is appropriate for the unit you are in to "with" the
:unit that you think you need.

I disagree. An Eiffel software engineer thinks about this when they *use* a 
module. 


Don.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Don Harrison             donh@syd.csa.com.au