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Posted by Jerry Stuckle on 07/31/07 01:20
Rik wrote:
> On Tue, 31 Jul 2007 02:38:04 +0200, Jerry Stuckle
> <jstucklex@attglobal.net> wrote:
>> I take this back - the result of the operation is unpredictable.
>> That's because:
>>
>> $rank[$i] = trim($rank[$i++]);
>>
>> $rank[$i++]
>>
>> is evaluated as $rank[$i]. However, when
>>
>> $rank[$i]
>>
>> is evaluated, does it use the old or the new version of $i?
>
> This is indeed dubious. Which of the '[' gets evaluated first?
> Allthough, left-associtivity might indicate the first one should be
> evaluated first (PHP4 behaviour).
>
> However, for:
>
> $array[$i] = $i++;
>
> Precedence as defined should kick in clearly. The '[' isn't in the table
> just for show.
>
>> The bottom line: don't change a value and use it in the same
>> statement. Results are unpredictable.
>
> And makes for more readable code indeed. However, if I read the
> documentation I fully expect the PHP4 result from my example, not the
> PHP5 one...
> --Rik Wasmus
Rik,
The key here is, precedence defines the order of OPERATOR evaluation -
but not the order of OPERAND evaluation. A subtle, but important
difference in cases like this.
For instance, it defines that '++' will be evaluated before '[]', it
doesn't define whether [$i] will use the old or new value of $i++. So
even though [$i] is evaluated before [$i++], $i++ is evaluated first and
the value of $i is unpredictable.
--
==================
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attglobal.net
==================
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