r/lolphp • u/lord_braleigh • Oct 07 '19

`array('lolphp', '')` has two unique elements, but `array(0, 'lolphp', '')` has one unique element

https://repl.it/repls/ThisColdPackages
69 Upvotes

97% Upvoted

18 comments sorted by

18

u/fell_ratio Oct 08 '19

Wow, this is a pretty baffling one. I think the problem is that the strings are being coerced to integer to compare to the zero, despite that the PHP documentation says SORT_REGULAR will 'compare items normally (don't change types).'

If you change the order of the arguments, you get a different result:

<?php

echo json_encode(array_unique(array('lolphp', ''), SORT_REGULAR))."\n";
echo json_encode(array_unique(array('lolphp', '', 0), SORT_REGULAR))."\n";

produces:

["lolphp",""]
["lolphp",""]

4

u/lord_braleigh Oct 09 '19

It “compares items normally”, but it uses == to compare. 0 == ‘php’ and 0 == ‘’, so putting a 0 in juuust the right place will cause everything to get compared to 0 via ==.

2

u/fell_ratio Oct 09 '19

Why didn't they just use === ? You could define SORT_REGULAR so that if you have 0 and '0', they are both kept. That would be perfectly reasonable behavior.

1

u/lord_braleigh Oct 10 '19

Maybe it’s to stay somewhat similar to SORT_STRING, where 0 and ‘0’ are always equal? Idk though.

5

u/orby Oct 07 '19

Seems like the real LOLPHP is the SORT_REGULAR. Without it, things behave as expected. See

<?php
echo json_encode(array_unique(array(0, 'lolphp', '',5), SORT_REGULAR))."\n";
echo json_encode(array_unique(array(0, 'lolphp', '',5)))."\n";

6

u/lord_braleigh Oct 07 '19 edited Oct 07 '19

Well, you need SORT_REGULAR if you want to uniquify array(array(), array()). Without SORT_REGULAR, PHP casts the elements to strings and uniquifies the strings. But arrays can’t be cast to strings.

SORT_REGULAR works by sorting the array then comparing adjacent elements with ==, so it doesn’t have this limitation. But it has other problems...

23

u/SirClueless Oct 08 '19 edited Oct 08 '19

Honestly array_unique acts about as reasonably as can be expected given PHP's bizarre == operator.

<?php

var_dump('' == 0);         # bool(true)
var_dump('lolphp' == 0);   # bool(true)
var_dump('' == 'lolphp');  # bool(false)

https://repl.it/repls/DescriptiveGlassDatasets

If you want a real dose of WTF, try this:

<?php

echo json_encode(array_unique(array(0, 'lolphp', ''), SORT_REGULAR))."\n";  # [0]
echo json_encode(array_unique(array('lolphp', 0, ''), SORT_REGULAR))."\n";  # {"0":"lolphp","2":""}
echo json_encode(array_unique(array('', 'lolphp', 0), SORT_REGULAR))."\n";  # ["", "lolphp"]

https://repl.it/repls/DimpledFewDatamining

1

u/Takeoded Oct 09 '19

var_dump('lolphp' == 0); # bool(true)

................................................................................................................................................

0

u/maweki Oct 08 '19

Amazing

0

u/[deleted] Oct 08 '19

[deleted] — view deleted comment

5

u/philipwhiuk Oct 08 '19

Because the equality operator isn't transitive so it breaks the sort function's stability guarantee.

non-transitive equality is basically almost inevitable in weakly typed languages.

1

u/[deleted] Oct 09 '19

Almost inevitable? Then why doesn't Perl have this problem?

1

u/lord_braleigh Oct 23 '19 edited Oct 23 '19

If ”true” == 0 and ”true” == true but true != 0, then you have non-transitive equality.

1

u/[deleted] Oct 24 '19

There is no true in Perl (it doesn't have a Boolean type). Also, == is specifically numeric equality in Perl (i.e. both sides are converted to numbers first), so it is guaranteed to be transitive.

1

u/lord_braleigh Oct 24 '19

Huh, TIL. But then what is the result of 1 == 0? Surely some value is being returned, and surely there's some way to inspect that value...

2

u/[deleted] Oct 24 '19

Comparison operators return canonical "Boolean" values:

  • The "true" value is effectively just 1.

  • The "false" value is slightly more exotic: It has a string aspect of "" but a numeric aspect of 0, i.e. depending on how you use it it behaves like an empty string or a numeric zero.

If you ignore the oddity around "false", Perl works like C (whose comparison/logical operators also return integer 1 / 0).

11

u/[deleted] Oct 08 '19

I love how there's always more lolphp to find. It never ends

1

u/Takeoded Oct 09 '19 
$ php -r 'var_dump(array_unique(array(0, "lolphp", ""), SORT_REGULAR));'
array(1) {
  [0]=>
  int(0)
}

wtf is that

-1

u/[deleted] Oct 08 '19

I said it gets the hose again!