division by zero is barely legal, but so false!

php > $a = 2/0;
PHP Warning: Division by zero in php shell code on line 1
php > var_dump( $a );
bool(false)

Random encounter: empty and indexing strings

php > $a = "I'm a string";
php > var_dump( empty($a['i am an index']) );
bool(false)

php > $a = "0I'm a string";
php > var_dump( empty($a['i am an index']) );
bool(true)

php > $a = " I'm a string";
php > var_dump( empty($a['i am an index']) );
bool(false)

And another inspired result:


$str = "a 0-gravity cat";
var_dump(empty($str['does not exist'])); // false
var_dump(empty($str['2 bottles of beer ...'])); // true
var_dump(empty($str['0x2 is numbericly!'])); // false
var_dump(empty($str['02 is numbericly!'])); // true
var_dump($str['010 numbericly!']); // y
var_dump("0x2" == 2); // true
var_dump("0x2" == "2"); // famously true

And just another finding investigating the issue even more:

php > var_dump( (int)'0x2' );
int(0)
php > var_dump( (int)'0x2' );
int(0)
php > var_dump( floor('0x2') );
float(2)
php > var_dump( (float)'0x2' );
float(0)

What else do I have to write?

All animals are ==, but some animals are === than others.

Equality comparators work differently when it comes to types. Arrays of different instances are always equal (see previous post), objects of different instances are ==-equal but not ===-equal. Funnily, comparing classes (or functions) to strings turns out to be equal again (because identifiers are nothing more than strings ).

<?

$a = array(1,2,3);
$b = array(2,3);

var_dump($a==$b); // false
var_dump($a===$b); // false
array_shift($a); // $a = (2,3)
var_dump($a==$b); // true
var_dump($a===$b); // true (!)

$x = new StdClass();
$y = new StdClass();

var_dump($x == $y); // true
var_dump($x === $y); // false

class X {};

$p = new X();
$q = new X();

var_dump($p == $q); // true
var_dump($p === $q); // false

$r = array();

var_dump($p == $r); // false
var_dump($p === $r); // false

var_dump("X" == X); // true
var_dump("X" === X); // true