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Bug #53724 array_diff like methods compares false as identity and true as equal
Submitted: 2011-01-12 14:16 UTC Modified: 2015-05-08 21:12 UTC
Avg. Score:5.0 ± 0.0
Reproduced:1 of 1 (100.0%)
Same Version:0 (0.0%)
Same OS:0 (0.0%)
From: lukas dot starecek at centrum dot cz Assigned: cmb (profile)
Status: Not a bug Package: Arrays related
PHP Version: 5.3.5 OS: Irrelevant
Private report: No CVE-ID: None
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 [2011-01-12 14:16 UTC] lukas dot starecek at centrum dot cz
array_diff functions compares boolean false as identity (operator "===") and boolean true as equal (operator "==") so behaves inconsistently. It should compare all values in same way and in my opinion it should compare as equals ("==") or have argument (or another mechanism) how to set whether compare by equal or identity.

As example I use array_diff_assoc but I think it will probably behave simmilary with another array realted functions (array_diff%, array_intersect%). In expected result I suppose comparing as equal (operator '==').

In example you can see, that array_diff_assoc behaves in such way that 0 or '0' or '' is not same as false, but 1 or '1' is same as true. So false is compared like '===' and true is compared like '=='. Because 0 is same as '0' and 1 is same as '1' I suppose, that this problem is only for boolean false value.

Test script:
$arr1 = array('a' => 0,     'b' => 1,    'c' => '0',   'd' => '1',  'e' => '',    'f' => false, 'g' => true, 'h' => 0,   'i' => 1);
$arr2 = array('a' => false, 'b' => true, 'c' => false, 'd' => true, 'e' => false, 'f' => false, 'g' => true, 'h' => '0', 'i' => '1');

var_dump(array_diff_assoc($arr1, $arr2));

Expected result:
array(0) {

Actual result:
array(2) {
  string(1) "0"


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 [2011-01-12 14:27 UTC] lukas dot starecek at centrum dot cz
A little mistake, '' behaves as same with false, so problem is only in comparing 0 and '0' (and maybee some other variables I did not used).
 [2011-02-20 16:20 UTC] tbrasta at gmail dot com
This is not a bug. The function is operating exactly as stated in the documentation, i.e. casted to string values are compared. Since (string) 0 = "0", (string) false = "" and (string) "0" = "0" but "0" !== "", you get the result as it should be.
 [2011-02-21 23:23 UTC] lukas dot starecek at centrum dot cz
Ah I did not noticed this "grey" part of method documentation in examples. You are right, documentation says it, but imho in not so clear way. I have read only specifications, not examples. Imho documentation could be a little bit more exact, because this is important.

So sadly this functions are designed only for string comparison, not for general variable comparison :-/ .

My fault, bogus, sorry. But think about functions of this kind for general variables comparison, not only for string comparison :-) .
 [2015-05-08 21:12 UTC]
-Status: Open +Status: Not a bug -Assigned To: +Assigned To: cmb
 [2015-05-08 21:12 UTC]
As tbrasta has already explained, this is not a bug. I agree, though, that the documentation of array_diff() should be improved, by linking to array_diff_uassoc(), array_udiff_assoc() and array_udiff_uassoc() in the "see also" section. I've submitted a respective patch via the online editor.
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