Calculate hash of an object

In PHP, sometimes you need to identify an object using a consistent string based on its internal values. The standard function spl_object_hash() isn’t always suitable because its result can change over time. To create a stable hash, you can use the following method:

class Foo {
 private $p;
 public function setProperty($p) {
  $this->p = $p;
 }
 // Calculates the object's hash based on the values of its properties
 public function __toString() {
  return md5(http_build_query(get_object_vars($this)));
 }
}

To get the hash, simply do:

$bar = new Foo();
$bar->setProperty('25');
echo $bar;
$hash = (string) $bar;

This approach ensures that the hash remains consistent and unchanged as long as the object’s property values do not change.