Re: In-Out Parameters for functions

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

Hyman Rosen wrote:

> Robert I. Eachus wrote:
> 
>> Hyman Rosen wrote:
>>
>>> In any case, when I
>>> said that a + b becomes "+"(a, b) and not "+"(b, a)
>>> I was not "absolutely wrong" but "absolutely right".
>>
>>
>> No, you were absolutely wrong as usual.  The order of evaluation of 
>> the parameters to "+" is undefined whether the "+" is user defined or 
>> language defined.
> 
> 
> Where did I say that the order of evaluation of the operands was
> defined? V'G'H argued that the philosophy of Ada was that a + b
> and b + a are the same. I pointed out that for user-defined "+",
> when you write a + b, the function is called with a as the Left
> operand and b as the Right, never the reverse.
> 
>  > I should stop wrestling with pigs.
> 
> You are so eager to believe I am wrong about everything I say that
> you are not reading what I say. Stop it. You're just going to annoy
> the pig :-)

No, it is trying to teach a pig to sing that annoys the pig.  When you 
wrestle with pigs, you just get dirty, and the pig enjoys it.  (Of 
course, if the pig is a pet and kept clean, the person doing the 
wrestling may stay clean and actually want the pig to enjoy it.)  But 
this is not a discussion of ENGLISH semantics ;-)

MY point, which apparently you missed, was not that Ada compilers are 
allowed to ignore the order of parameters (except of course with named 
notation). It is that you will find lots of places in the standard where 
order independent SEMANTICS occurs, for example in 13.7.1(7).  In those 
cases the usual implementation (in this case of package 
System.Storage_Elements) will simplify things by using parameter 
flipping and pragma Inline.  If we were to change the semantics of Ada 
to require left-to-right evaluation, what should be done with these 
functions, especially when they are in-lined?  A workable rule probably 
could be written, but it is the sort of thing you have to look at with a 
proposal like yours.

-- 
                                           Robert I. Eachus

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