Re: Possible Ada deficiency?

[Jeffrey Carter <spam@spam.com>]

Robert A Duff wrote:

> What rule would you prefer (in a from-scratch language design)?

That's hard to tell, since I haven't really designed such a language. 
Perhaps simply that the rule for a private type may be different from 
the rule if the full type were visible. That would allow compilers to 
implement a private type as a secret access type, but not prevent 
compilers from using other approaches, such as looking at the full type 
in the body and using that information, or allocating objects 
dynamically at run time.

> The main thing I dislike about the Ada rule is that it is possible to
> write code by accident that behaves differently because one compiler
> chooses pass-by-copy and another one pass-by-reference.  And it's not
> clear whose responsibility it is to worry about this kind of bug: should
> procedures be written so that they work even in the presence of aliasing
> among actual parameters?  Or should callers avoid that aliasing?  And
> what can the caller know about data modified in a procedure that raised
> an exception in the middle of processing?

It seems pretty clear to me that it's the procedure's responsibility. 
Code that relies on the parameter-passing mechanism for types with an 
undefined mechanism has an error.

-- 
Jeff Carter
"You cheesy lot of second-hand electric donkey-bottom biters."
Monty Python & the Holy Grail
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