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Re: OT: and even in Dart .........Re: simple session question [message #175910 is a reply to message #175724] Sat, 05 November 2011 20:04 Go to previous messageGo to previous message
Peter H. Coffin is currently offline  Peter H. Coffin
Messages: 245
Registered: September 2010
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Senior Member
On Sat, 22 Oct 2011 16:08:01 -0400, Norman Peelman wrote:
> On 10/22/2011 01:34 PM, Thomas Mlynarczyk wrote:
>> Luuk schrieb:
>>> i did send a bug-report:
>>> https://bugs.php.net/bug.php?id=60114
>>
>> I do not see any bug here. I was confused because it's a crappy way to
>> code, but it's clear why it works the way it does:
>>
>> $foo = 0;
>> $foo = $foo++;
>>
>> is definitely identical to
>>
>> $foo = 0;
>> $foo = ($foo++);
>>
>> since ++ has higher precedence than =. In fact, ($foo = $foo)++ does
>> rightfully throw a parse error, since you can only increment a variable,
>> not an expression.
>>
>> As mentioned before in this thread, the above code is equivalent to
>>
>> $foo = 0;
>> $tmp = $foo; // $foo++ yields the previous value, which is 0
>> $foo = $foo + 1; // then $foo is incremented...
>> $foo = $tmp; // ...and then re-assigned the old value
>>
>> It's the exact same procedure as it would be with $foo = $bar++.
>>
>> Greetings,
>> Thomas
>>
>
> No they are not the same.
>
> $foo = 0;
> $foo = $foo++;
>
> It should be equivalent to:
>
> $foo = 0; // 0
> $foo = $foo; // 0 = 0
> $foo = $foo + 1; // 0 = (0 + 1)
>
> $foo++ means that the variable is to be incremented after the variable
> is accessed. Something is clobbering that increment.

Yes. The ASSIGNMENT back to $foo is clobbering it. The increment happens
immediately after access, before the VALUE is passed back to the
assignment.

> ++$foo means that the variable is to be incremented piror to the
> variable being accessed. Works as expected.
>
>
> Haven't seen the source code but there must be some temporary
> variable that's getting clobbered for the $foo++ example.

It's just happening in the proper order. increment happens before
assignment, exactly per
http://php.net/manual/en/language.operators.precedence.php

The catch is that the assignment is destroying the increment, because
the variable access happened BEFORE the increment.

--
17. When I employ people as advisors, I will occasionally listen to
their advice.
--Peter Anspach's list of things to do as an Evil Overlord

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