In-Out Parameters for functions (was: Re: Certified C compilers for safety-critical embedded systems

[Marin David Condic <nobody@noplace.com>]

Yeah, but as far as I can tell C always had "in only" parameters and 
everything was a function returning a result. The only way you could get 
"in out" mode was passing addresses (indistinguishable to the garden 
variety programmer from a 'Access) and of course dealing with all the 
errors that resulted from no checking that a parameter actually was an 
address. Such a setup didn't seem to hurt C with respect to popularity 
or getting Fortran programmers to understand it.

I'm ambivalent about "in out" for functions. I've never found it 
difficult to use functions just the way they are and can't think of a 
case where in-out would have helped me with a real world problem. The 
only example anyone ever seems to cite is the Random Number Generator 
leading me to think that maybe this *is* the only instance in which it 
is genuinely useful. OTOH, I could see how they might be included and 
not impact my life one iota. If you don't need it, you don't use it. 
Except that possibly it casts into doubt what happens in an expression 
loaded with function calls where one used to be able to assume that the 
parameters were not being modified. With in-out you'd have to know the 
parameter modes before you could interpret what the expression was doing.

MDC



Robert A Duff wrote:
> 
> As far as I can remember, this idea was considered, and was generally
> thought to be ugly.  I mean, suppose you're trying to convince a Fortran
> programmer to use Ada for numerics stuff.  If you start babbling about
> aliased and 'Access when there is no inherent need for pointers,
> they're going to laugh, and rightly so.
> 



-- 
======================================================================
Marin David Condic
I work for: http://www.belcan.com/
My project is: http://www.jsf.mil/NSFrames.htm

Send Replies To: m   o   d   c @ a   m   o   g
                    c   n   i       c   .   r

     "Face it ladies, its not the dress that makes you look fat.
     Its the FAT that makes you look fat."

         --  Al Bundy

======================================================================