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Date: Wed, 1 Dec 2021 14:19:07 +0000
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To: =?UTF-8?B?QW5kcsOpIEjDpG5zZWw=?= <andre@webkr.de>
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Subject: Re: [PHP-DEV] Array comparison works completely different than documented?
From: george.banyard@gmail.com ("G. P. B.")

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On Wed, 1 Dec 2021 at 13:56, Andr=C3=A9 H=C3=A4nsel <andre@webkr.de> wrote:

> The official documentation contains a conceptual description of array
> comparison in
> https://www.php.net/manual/en/language.operators.comparison.php#example-1=
13
> .
>
> Curiously the people who wrote the inofficial spec (I think the HHVM team
> at
> Facebook?) came to
> pretty much the same result, described in
>
> https://github.com/php/php-langspec/blob/master/spec/10-expressions.md#re=
lat
> ional-operators
> <https://github.com/php/php-langspec/blob/master/spec/10-expressions.md#r=
elational-operators>
> :
>
> > If both operands have array type, if the arrays have different numbers =
of
> elements, the one
> > with the fewer is considered less-than the other one, regardless of the
> keys and values in each,
> > and the comparison ends. For arrays having the same numbers of elements=
,
> the keys from the left
> > operand are considered one by one, if the next key in the left-hand
> operand exists in the
> > right-hand operand, the corresponding values are compared. If they are
> unequal, the array
> > containing the lesser value is considered less-than the other one, and
> the
> comparison ends;
> > otherwise, the process is repeated with the next element. If the next k=
ey
> in the left-hand
> > operand does not exist in the right-hand operand, the arrays cannot be
> compared and FALSE is
> > returned. If all the values are equal, then the arrays are considered
> equal.
>
> In reality, array comparison works completely different, it is however
> unclear to me how exactly
> it does work: https://3v4l.org/630vG
>
> Do we know how this happened?
>
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>

It seems the docs are not accurate in that it will not try to find the
corresponding element in the second array.

By rearranging the keys to be defined in the same order the docs seems to
match the corresponding behaviour: https://3v4l.org/2ta2k

The actual C code implementation of how the arrays are compared (after some
symbol navigation) is the zend_hash_compare_impl() function.
https://heap.space/xref/php-src/Zend/zend_hash.c?r=3Dd3f073e8#2919

Hope this helps.

Best regards

George P. Banyard

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