# Array comparison works completely different than documented? - Thread: https://externals.io/message/116547 - Original archive: https://news-web.php.net/php.internals/116547 - Started by andre@webkr.de on 2021-12-01T13:56:07+00:00 - Messages: 5 - Reply by email to internals@lists.php.net - More for agents: search with https://externals.io/search.md?q={query} · JSON API at https://externals.io/api · documentation at https://externals.io/llms.txt --- ## #116547 — andre@webkr.de — 2021-12-01T13:56:07+00:00 URL: https://externals.io/message/116547#116547 The official documentation contains a conceptual description of array comparison in https://www.php.net/manual/en/language.operators.comparison.php#example-113. 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#relat ional-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 key 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? --- ## #116548 — G. P. B. — 2021-12-01T14:19:07+00:00 URL: https://externals.io/message/116547#116548 · In reply to: #116547 > The official documentation contains a conceptual description of array > comparison in > https://www.php.net/manual/en/language.operators.comparison.php#example-113 > . > > 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#relat > ional-operators > > : > > > […] > elements, the one > > […] > keys and values in each, > > […] > the keys from the left > > […] > operand exists in the > > […] > unequal, the array > > […] > the > comparison ends; > > […] > in the left-hand > > […] > compared and `FALSE` is > > […] > 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? > > -- > > To unsubscribe, visit: https://www.php.net/unsub.php > 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=d3f073e8#2919 Hope this helps. Best regards George P. Banyard --- ## #116549 — Christoph M. Becker — 2021-12-01T14:59:48+00:00 URL: https://externals.io/message/116547#116549 · In reply to: #116547 > The official documentation contains a conceptual description of array > comparison in > https://www.php.net/manual/en/language.operators.comparison.php#example-113. > > 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#relat > ional-operators: > > > […] > elements, the one > > […] > keys and values in each, > > […] > the keys from the left > > […] > operand exists in the > > […] > unequal, the array > > […] > comparison ends; > > […] > in the left-hand > > […] > compared and `FALSE` is > > […] > equal. > > In reality, array comparison works completely different, it is however > unclear to me how exactly > it does work: https://3v4l.org/630vG The point is that $a > $b is actually checking whether $b <= $a. This is fine for ordered values, but these arrays are not orderable (according to PHP's comparison). That might indeed not be documented in the PHP manual (the language specification appears to be abandoned anyway). -- Christoph M. Becker --- ## #116552 — Benjamin Morel — 2021-12-01T23:24:13+00:00 URL: https://externals.io/message/116547#116552 · In reply to: #116549 > > The point is that $a > $b is actually checking whether $b <= $a. This > is fine for ordered values, but these arrays are not orderable > (according to PHP's comparison). That might indeed not be documented in > the PHP manual (the language specification appears to be abandoned anyway). Shouldn't we throw an exception when comparing arrays with <, <=, >, >= anyway? - Benjamin --- ## #116567 — Jordan LeDoux — 2021-12-05T00:43:48+00:00 URL: https://externals.io/message/116547#116567 · In reply to: #116549 On Wed, Dec 1, 2021 at 7:00 AM Christoph M. Becker wrote: > > The point is that $a > $b is actually checking whether $b <= $a. This > is fine for ordered values, but these arrays are not orderable > (according to PHP's comparison). That might indeed not be documented in > the PHP manual (the language specification appears to be abandoned anyway). > > Are there any tests that capture this? As part of my operator overload RFC I'm breaking out > into its own opcode instead of a reordered <=, so this may actually be "fixed" by this. However, I haven't noticed any array related comparison tests failing in my builds. Jordan