Re: time / update problem

Frederic Merizen wrote:
>>Hello,
>>
>>what should the following code print?
>>
>>class MAIN
>>creation
>>   make
>>feature
>>   make is
>>      local
>>         now: TIME
>>      do
>>         create c.make
>>         now.update
>>         c.never.update  -- is this ever executed???
>>         io.put_string(c.never.elapsed_seconds(now).out + "%N")
>>      end
>>   c: CC
>>end
>>
>>class
>>   CC
>>creation
>>   make
>>feature
>>   make is do end
>>   never: TIME
>>end
>>
>>In my eyes it should be close to 0, but it seems that the line
>>c.never.update is never done. Is this an invalid call for some reason or
>>yet another optimizer bug?
> 
> 
> TIME is an expanded class, so the qualified call 'c.never' returns a copy of 
> the attribute. The call to 'update' only updates the copy.
> 
> I'd say there's a dessign lesson here: "think twice before creating mutable 
> expanded classes" (such as TIME - but I do not intend to specifically 
> criticize TIME here. There may well be good reasons for this choice in the 
> case of TIME - maybe a performance tradeoff. I don't know for sure, I wasn't 
> on the team yet when that class was written.)
I think you are perfectly right: I made a mistake in TIME and we should
remove all modifications procedures from class TIME.
May be a strict simple rule about expanded classes would be to disallow
all modification procedures ?
Is this simple rule too strict ?

If modification procedures remains allowed, I think we should add a new
check in the compiler to avoid this terrible pitfall of user-defined
expanded.

Note for SmartEiffel developpers: a new visitor like the one we have for 
example to check exports could check that the expanded is not used for 
writing... if you see what I mean.
Using the same idea, we should also check the code of all dispose 
routine to see if the disposed object is not passed away.

Note for everybody: we won't change rules about user-expanded classes
in release 2.2. (Stay cool.)
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