Edit report at https://bugs.php.net/bug.php?id=29992&edit=1
ID: 29992
Comment by: looris at gmail dot com
Reported by: fletch at pobox dot com
Summary: foreach by reference corrupts the array
Status: Not a bug
Type: Bug
Package: Scripting Engine problem
Operating System: linux
PHP Version: 5.0.1
Block user comment: N
Private report: N
New Comment:
No one cares about the technical explanation about why this happens at a low
level. I'm quite puzzled you are still in denial about this bug.
Previous Comments:
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[2012-02-09 16:49:22] rasmus@php.net
No matter how you paint this, it isn't a bug. What you are really asking for is
some sort of block-level scoping. As such, it should be proposed as a feature
request, but it would be a major change in the language. The simplest way to
illustrate that is to just unroll the loops. Take this example:
$a = array(1,2);
foreach($a as &$b) { }
foreach($a as $b) { }
print_r($a);
The problem here is that people find it inconsistent that the 2nd loop changes
$a. But if we unroll the loops and write the exactly equivalent code without the
foreach construct we get:
$a = array(1,2);
// First loop, $b is a reference to each element in $a
$b = &$a[0];
$b = &$a[1];
// Second loop, $b is assigned the value of each element in $a
$b = $a[0];
$b = $a[1];
Those two pieces of code are identical in every way. The thing that confuses
people is that $b is still a reference $a[1] going into the second loop.
Since PHP doesn't have block-level scoping, there is nothing in the language
that would permit $b to be unset between the two loops without introducing a
major inconsistency. In fact there is plenty of code that relies on this fact
which would break if we made such an arbitrary change.
I suppose what you are asking for is syntax along the lines of:
$a = array(1,2);
{
local $b = &$a[0];
$b = &$a[1];
}
{
local $b = $a[0];
$b = $a[1];
}
Where $b is locally scoped in each of those blocks and it might look like this
in a foreach case:
$a = array(1,2);
foreach($a as local &$b) { }
foreach($a as local $b) { }
Without such a scoping syntax change, something as simple as:
forach(array(1,2,3) as $b) { }
echo $b;
where the code fully expects $b to be 3 would break.
------------------------------------------------------------------------
[2012-02-09 12:33:40] robbie at shapehq dot co dot uk
I feel very strongly that this behavior is wrong. It's not consistent with other languages and
will cause great confusion!
------------------------------------------------------------------------
[2011-10-20 04:56:50] bruce at kaskubar dot com
With all due respect to those who spend their time developing, debugging, and explaining PHP,
BALDERDASH!
Elsewhere, those of us who continue to claim "bug" are supposed to be chastened by all the
explanations that have been provided over the years. The fact that the reports persist and the
explanations grow is evidence contrary to the finding of Bogus and in support of what is expected
behavior.
Fletch's example, for example, is real and reproducible through at least v5.3.2.
How in the world can it be expected for a (second) loop and its object to perform as though no
related instructions were executed previously, and then for that interaction to raise its ugly head
for only the last iteration? It cannot be. It can be explained. But so can an earthquake be. That
doesn't make it expected.
I am unaware of any other case where prior use of a variable affects subsequent use of the
same-named variable where its value is being explicitly reset or, as in the case of foreach,
implicitly reset by virtue of its purpose. (That is, we can use $i as a loop counter here and as a
file handle there and as long as we don't cross their purposes in the space-time continuum, all
is well.)
The only bogus thing about this bug report and all its cousins is their shared status.
------------------------------------------------------------------------
[2011-09-02 15:13:42] publcishady at gmail dot com
If you describe how it works that's not an excuse for unexpected results. I understand why the
last element becomes a reference, but I don't understand why it SHOULD become a reference.
That's obviously a bug for me.
------------------------------------------------------------------------
[2011-07-18 05:03:24] martijn at twotribes dot com
Well, it is expected by the people who designed the language perhaps, but not by me. Iterating
through an array, without doing anything, shouldn't change the array. Period. If I do something
similar in another language like C++, this will never be the result.
------------------------------------------------------------------------
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