Re: Ada style of passing 'in' parameters considered dangerous?

[gautier_niouzes@hotmail.com (Gautier)]

James S. Rogers

> In Ada an IN parameter is treated as a constant within the subprogram
> it is passed to. This eliminates the ability to shoot yourself in the foot
> with an IN parameter.

As Robert metioned, you can: an IN parameter and an IN OUT may
reference the same object. In this situation, ypeee: you believe
that your IN parameter is like a rock-solid, unalterable constant,
but in fact it is being peacefully modified in the procedure itself!

> I have never seen a case where Ada parameter modes have
> shot the programmer in the foot.

I have seen a case of translation (from Modula) where a lot
of procedures were behaving wrong because of the above problem.
Passed-by-copy parameters were translated into "in" parameters,
so their eventual direct modifications were detected at compile-time,
and an explicit copy was added (e.g. procedure P(a:T) is aa:T:= a; ...).
But there were cases with "Q(a,b:T; c:in out T);" and calls like
"Q(a,b,a)". :-) Not a warning from any compiler!
________________________________________________________
Gautier  --  http://www.mysunrise.ch/users/gdm/gsoft.htm

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