Re: In-Out Parameters for functions

["Robert I. Eachus" <rieachus@comcast.net>]

Vinzent 'Gadget' Hoefler wrote:

> Hyman Rosen wrote:
> 
>> For the particular case of sqrt(x), where we're talking about Ada's
>> built-in sqrt, and the only possible side-effect is for it to raise
>> an exception. But if instead we have (gnurble(x) > 0.5 and b), and
>> the compiler knows that b is false but has no information about
>> what gnurble does, it must call gnurble(x) even though the result
>> is irrelevant.
> 
> 
> Yes, it should (I'm not sure, if it actually *has to*) call the 
> function if it is possible that the function has side-effects.
> 
> What's your problem here?
> 

That he has never read 10.2.1(18)? "If a library unit is declared pure,
then the implementation is permitted to omit a call on a library-level 
subprogram of the library unit if the results are not needed after the 
call. Similarly, it may omit such a call and simply reuse the results 
produced by an earlier call on the same subprogram, provided that none 
of the parameters are of a limited type, and the addresses and values of 
all by-reference actual parameters, and the values of all by-copy-in 
actual parameters, are the same as they were at the earlier call. This 
permission applies even if the subprogram produces other side effects 
when called."

Can't we just all agree that Hymen is not an Ada language expert and 
doesn't want to be?  In this case, the rules of Ada are well thought out 
to allow any user, not the compiler to determine whether an 
"unnecessary" function call can be eliminated.  Similarly, the language 
allows users to force syncronization points and orders of evaluation, 
when they are a necessary part of the algorithm being implemented.

We have jokingly called for shooting a programmer who knowingly writes 
code that depends on order of evaluation and then--yes that is an Ada 
and then--doesn't document it or force the compiler to use the necessary 
order.   Actually the correction applied would probably be education, 
warnings, bad reviews, and eventually firing the employee if nececssary.

For anyone who deliberately persists in such bad habits, if necessary 
could be within weeks. Emphasis on deliberately, but I have had to make 
that decision for programmers who persisted in other bad habits like 
bypassing the required check-in procedures for software. In that case, 
firing the programmer probably saved him from a lynch mob, as other 
programmmers kept finding their submissions being rejected due to his 
changes not passing the regression tests.

What do we do with Mr. Hymen Rosen?  For now, I'm going to just post 
chapter and verse, and that Mr. Rosen's opinion on any Ada language 
issue should be ignored.

-- 
                                           Robert I. Eachus

"The only thing necessary for the triumph of evil is for good men to do
nothing." --Edmund Burke