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Date: Wed, 04 Feb 2004 09:54:09 -0500
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Subject: Re: In-Out Parameters for functions
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Date: 2004-02-04T09:54:09-05:00
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David Starner wrote:
>>     p : Point := (x => ReadCoord, y => ReadCoord, z => ReadCoord);
> 
> I have some pieces of code in response:
> for I in 0.0 .. 1.0 step 0.25

Is this currently legal in Ada? Remember that my example is.

> the fact that x may have been passed by copy or by reference.

OK, I accept that there are more ambiguity issues than I have
been cnsidering. I suppose you object to getting rid of those too?

> In any real program, diddling with a bunch of global variables is likely
> to be hard to maintain and hard to reason about.

But using functions that read input is not hard to reason about.
     BunchOfReadings : array(1..100) of Integer := (others => ReadSensor);
Someone might reasonably think that the above line of code should fill
the array with sensor readings in order. You can tell him that it won't
work that way, but you can hardly say that he had no right to expect that
it would.

> sequence points where most languages don't have them

Java does, and many people are now exposed to that.
The Java language refernce manual also recommends not writing code
which exploits this, though, so that's one for your side. I think
it's just atavistic dread from the reptillian hindbrain.

 > it's a loss of an optimization opportunity

But it's not, except for programs which are now exhibiting unspecified
behavior. If an expression has only one value regardless of execution
order, then the compiler will be free to evaluate it in any order.