Question

I’m wondering why the PHP language allows implicit property declaration when most languages need to define properties within the class declaration itself (see code below). Is there a practical use for this type of coding style?

$user1 = new User();
$user1->name = "Kylie";
echo $user1->name;

class User{}

Answer 1

The use-case are value objects

$a = new stdClass;
$a->something = 12;
$a->somethingElse = 'Hello World';
myFunction ($a);

This allows to create some objects, that just carry around structured data (something like structs in other languages), without the need to define a class for it.

Another point is, that — because PHP is weakly-typed anyway — there is no real reason to forbid it. If you need something stronger, overweite __set()

public function __set ($propertyName, $value) {
  throw new Exception("Undefined Property $propertyName");
}