ID: 21702
User updated by: [EMAIL PROTECTED]
Reported By: [EMAIL PROTECTED]
Status: Open
Bug Type: Scripting Engine problem
Operating System: Any
PHP Version: Any
New Comment:
> Although I admit that the behaviour is quite inconsistent,
> we won't fix this anyway because the issue's all up to the
> language design.
Well, I dunno. In bug #8353, [EMAIL PROTECTED] says: "...the following
note exists in the foreach() entry of the manual and has for over two
years:
Note: Also note that foreach operates on a copy of the specified
array, not the array itself, therefore the array pointer is not
modified as with the each() construct and changes to the array element
returned are not reflected in the original array."
The documentation has been changed very recently.
To me, this seems like re-defining the language. (Or "changing the
rules in the middle of the game", if you prefer.) Instead of fixing the
bug, you say it's a feature and change the docs. That seems very
Microsoft-ish. Plus, such a language construct is inconsistent,
unintuitive and seriously limited in usability.
> foreach statement always makes use of a copy of the given
> array instead of the original itself unless the array is a
> reference or has a reference.
The "makes a copy" part is in the docs, and is what I expect. The
"unless..." part is (still) not in the docs and seems non-sensical. In
fact, in "What References Do", the manual says about what happens after
"$a =& $b" the following: "Note: $a and $b are completely equal here,
that's not $a is pointing to $b or vice versa, that's $a and $b
pointing to the same place." Nowhere in the manual it says that
references are special. It just says that a reference is another name
for the same variable. I don't see why foreach treats them specially.
Note that I'm not advocating for changing the documentation; I'm
actually strongly supporting what the documentation says and has said
for a long time, and that means foreach is what needs to be changed.
BTW, does the "unless..." part of the above quotation mean that when I
do
$a =& $b;
foreach ($a as $elem)
$elem->change_self();
it will work - because foreach is not working with a copy of the array?
I suppose not, because it will surely make a copy of each element,
right? Can I then coerce it by first making an array of references to
every element, so that foreach will treat the elements specially?
Wow, this is even nastier than I thought! ;-)
Let's make a vote on the front page of php.net:
- Foreach Pro-consistency Front
program: repair foreach, return docs to previous state
- Conservative Foreach Party
program: keep foreach as is, make docs even more clear
Previous Comments:
------------------------------------------------------------------------
[2003-01-17 07:36:09] [EMAIL PROTECTED]
Although I admit that the behaviour is quite inconsistent, we won't fix
this anyway because the issue's all up to the language design.
> Also, I find this very inconsistent. I didn't mention it in the
original
> description, but you know what? When you nest two foreach's using
the
> VERY SAME variable, it magically works! How is it possible that two
> references to the same variable are somehow more equivalent than the
> variable is to itself??? :-o
Well, it looks like a magic.
To say more precisely, foreach statement always makes use of a copy of
the given array instead of the original itself unless the array is a
reference or has a reference.
That's the reason you could get along with nested foreach loops in
general case. Thus the following while loop (A) is an equivalent to
(B).
<?php /* A */
$copy_foo = $a;
reset($copy_foo);
while (list(,$b) = each($copy_foo)) {
$copy_bar = $a;
reset($copy_bar);
while (list(,$c) = each($copy_bar)) {
print $c;
}
}
?>
<?php /* B */
$a = array(1, 2);
foreach ($a as $b) {
foreach ($a as $c) {
print $c;
}
}
?>
Related bugs: http://bugs.php.net/bug.php?id=8353
------------------------------------------------------------------------
[2003-01-17 06:29:20] [EMAIL PROTECTED]
> Marking this as a documentation problem.
I was sooo very much afraid you would do exactly this! :-(
So it is really intended to work like this? You don't find there is
anything wrong with the foreach construct?
Consider this: this means that you CAN'T use foreach at all in cases
where you don't know for certain whether you couldn't have possibly
been called from a foreach over the same array (or a reference to it,
in fact).
Also, you CAN'T use foreach in a case like mine, in which I found this
problem:
foreach ($obj->arr as $elem) {
...
$obj->method($elem);
...
}
What if the method also wants to iterate over the array? You don't
know, it wasn't you who wrote the class library...
Also, I find this very inconsistent. I didn't mention it in the
original description, but you know what? When you nest two foreach's
using the VERY SAME variable, it magically works! How is it possible
that two references to the same variable are somehow more equivalent
than the variable is to itself??? :-o
No, I don't agree that this is just a documentation problem. Marking as
a scripting engine problem again. You may disagree, of course, but
please, give it a thought. Or perhaps some discussion. Thanks.
------------------------------------------------------------------------
[2003-01-17 06:20:26] [EMAIL PROTECTED]
Sorry, I meant the outer loop gets confused; not the deeper loop.
------------------------------------------------------------------------
[2003-01-17 02:23:31] [EMAIL PROTECTED]
Actually this is a dupe of bug #14607, but this PR is much more
concise than that, so I'm going to keep 14607 bogus and make this
alive.
Since foreach() uses "internal array pointer" and references are
designed
to share one such pointer, the deeper loop gets confused and your
script never
gives the expected result.
Virtually the script can be rewritten as...
<?php
$a = array(1, 2);
for ($ptr = 0; $ptr < count($a); $ptr++) {
$b = $a[$ptr];
echo "outer: $b <br />\n";
for ($ptr = 0; $ptr < count($a); $ptr++) {
$c = $a[$ptr];
echo "inner: $c <br />\n";
}
}
?>
Marking this as a documentation problem.
------------------------------------------------------------------------
[2003-01-16 20:05:14] [EMAIL PROTECTED]
Try this:
<?php
$a = array(1, 2);
$ref =& $a;
foreach ($ref as $b) {
echo "outer: $b<br>\n";
foreach ($a as $c)
echo "-- inner: $c<br>\n";
}
?>
The output is:
outer: 1
-- inner: 1
-- inner: 2
(i.e., the processing stops after the first iteration of the outer
foreach). If I understand the docs well, the output should be:
outer: 1
-- inner: 1
-- inner: 2
outer: 2
-- inner: 1
-- inner: 2
When you remove the ampersand from the assignment to $ref, it works as
expected.
The documentation is a bit unclear on this. It says "Also note that
foreach operates on a copy of the specified array, not the array
itself, therefore the array pointer is not modified as with the each()
construct...", which leads me to believe that the sample code should
work. But then it goes on to say: "However, the internal pointer of the
original array *is* advanced with the processing of the array.", which
seems to contradict the first quotation???
This is probably a dupe of bug #14607, but that one is closed as
"bogus" and I can't reopen it. Also see bug #5052, which is similar but
not quite, and it's closed.
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/?id=21702&edit=1
