Re: Design By Contract

[rodemann@mathematik.uni-ulm.de (Joerg Rodemann)]

Don Harrison (nospam@thanks.com.au) wrote:
> The thing is, though, that the designer of the supplier class *intends* the
> client to see the structure of attributes in just the same way as the author
> of an Ada interface *intends* clients to see the structure of a value
> returned
> by a function.

> Exporting happens on a need-to-know basis. If clients need attributes for 
> any purpose (including efficiency tuning), then the supplier exports them. 
> If they don't, then the supplier keeps them hidden. Note that in the
> extreme 
> case of an attribute whose underlying class exports none of its attributes, 
> you have the equivalent to an Ada private attribute. That is, the Ada

I wonder what this is all about? In Ada as well as in Eiffel you have to
decide if you grant a client read, read/write or none access to any member
variables of an object. Certainly the syntax of the following implementations
differ --- and in this case tend to need a few more characters in the Ada
version. Although there is a slight difference: in Ada you arrange one
or more 'class' definitions in a package whereas the feature mechanism of
Eiffel reminds me a little bit of the friend declarations in C++. (Sorry if
I got this wrong, I just had a short glance at Eiffel yet.) 

But at least I do not recognize any fundamental difference between the
explicit declaration of a function and the possibility to use a member 
variable as if it was a function. (As far as I remember there is some
construct in Ada where a similar interpretation is used. Perhaps someone
else has a better memory than me...must have been digging up too many
memory problems in C++ lately ;-> ) I occurs to me that the differences
this thread is all about start from a slight difference in writing. (You
use more words to say this, so mine is better. As in

   while ( cond ) {                      while cond loop
      ...                     vs.           ...
   }                                     end loop;

Well, of course just my opinion

Yours

Joerg

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rodemann@mathematik.uni-ulm.de | Dipl.-Phys. Joerg S. Rodemann
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