[RFC] Fix "foreach" behavior

Hi,

I'd like to start discussion about fixing inconsistent "foreach" statement
behavior.
The implementation is almost done. It not only fixes inconsistencies in a
defined by RFC way but also improves performance in most usual cases,
because now foreach by value over array doesn't require array duplication.

https://wiki.php.net/rfc/php7_foreach

https://github.com/php/php-src/pull/1034

I'm going to continue work on implementation improvement and may be fixing
related behavior of some internal functions when they used on array
iterated by foreach by reference (e.g. array_unshift()). However, the
conceptual behavior defined in RFC is not going to be changed anymore.

Thanks. Dmitry.

Nice job Dmitry, as usual !

Julien

Hi,

I'd like to start discussion about fixing inconsistent "foreach" statement
behavior.
The implementation is almost done. It not only fixes inconsistencies in a
defined by RFC way but also improves performance in most usual cases,
because now foreach by value over array doesn't require array duplication.

https://wiki.php.net/rfc/php7_foreach

https://github.com/php/php-src/pull/1034

I'm going to continue work on implementation improvement and may be fixing
related behavior of some internal functions when they used on array
iterated by foreach by reference (e.g. array_unshift()). However, the
conceptual behavior defined in RFC is not going to be changed anymore.

I think that I am raising a concern that is not real, but I'll do so anyway.

You write:

This will lead to copy-on-write on attempt of array modification inside the
loop.  As result, we will always iterate over elements of array originally
passed to foreach, ignoring any possible array changes.

I think that you mean modification of the array and that this does not relate to
modification of array elements. Ie will code like the following still work:

foreach($_POST as &$v)
$v = trim($v);

Otherwise - good.

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Hi,

Nikita got an idea about stopping changing of array/object internal
pointers even in forech by reference.
I've added an additional RFC section:

https://wiki.php.net/rfc/php7_foreach#additional_behavoir_change

Trivial implementation on top of the main patch:

https://gist.github.com/dstogov/63b269207ba0aed8b776

and an additional proposed voting question.

Also, the implementation now must be almost complete.

Thanks. Dmitry.

Hi,

I'd like to start discussion about fixing inconsistent "foreach" statement
behavior.
The implementation is almost done. It not only fixes inconsistencies in a
defined by RFC way but also improves performance in most usual cases,
because now foreach by value over array doesn't require array duplication.

https://wiki.php.net/rfc/php7_foreach

https://github.com/php/php-src/pull/1034

I'm going to continue work on implementation improvement and may be fixing
related behavior of some internal functions when they used on array
iterated by foreach by reference (e.g. array_unshift()). However, the
conceptual behavior defined in RFC is not going to be changed anymore.

Thanks. Dmitry.

Hi,

I'd like to start discussion about fixing inconsistent "foreach" statement
behavior.
The implementation is almost done. It not only fixes inconsistencies in a
defined by RFC way but also improves performance in most usual cases,
because now foreach by value over array doesn't require array duplication.

https://wiki.php.net/rfc/php7_foreach

https://github.com/php/php-src/pull/1034

I'm going to continue work on implementation improvement and may be fixing
related behavior of some internal functions when they used on array
iterated by foreach by reference (e.g. array_unshift()). However, the
conceptual behavior defined in RFC is not going to be changed anymore.

Thanks. Dmitry.

I think the new behavior introduced by this RFC is much more consistent
than what we have right now. Previously things depended on details of
refcounting and hashing and had very weird interaction with current() etc.
Now the behavior looks clear for all cases.

There's just one thing I'd like to discuss: The object by-value case:

Currently this is handled in much the same way as array by-reference, i.e.
changes to the object will influence iteration. Currently we can't
implement this any differently, however if we always use zend_array instead
of HashTable (and fully support refcounting for this), as has been
suggested in another thread, we could handle this case the same way as
arrays (i.e. just add a refcount to the properties zend_array). Assuming we
can implement it this way, I'm not totally sure which behavior makes more
sense. On one hand it would make arrays and plain objects work the same
way. On the other hand arrays and objects have different copying semantics
in other places as well.

Anyway, big +1 on this, thanks for implementing it.

Nikita