Currently it's possible to use class property that isn't even declared. This of course will produce no IDE auto-complete, but will work because PHP will declare such property dynamically.
It's considered bad practice because class declaration won't be exposing all it's properties. The solution from Phabricator is placing __set and __get methods in base class to ensure that in such cases an exception will the thrown. Example class: https://github.com/phacility/libphutil/blob/master/src/object/Phobject.php
<?php
/**
* Base class for libphutil objects. Enforces stricter object semantics than
* PHP.
*
* When a program attempts to write to an undeclared object property, PHP
* creates the property. However, in libphutil this is always an error (for
* example, a misspelled property name). Instead of permitting the write,
* subclasses will throw when an undeclared property is written.
*
* When a program attempts to iterate an object (for example, with `foreach`),
* PHP iterates its public members. However, in libphutil this is always an
* error (for example, iterating over the wrong variable). Instead of
* permitting the iteration, subclasses will throw when an object is iterated.
*
* (Legitimately iterable subclasses can provide a working implementation of
* Iterator instead.)
*/
abstract class Phobject implements Iterator {
public function __set($name, $value) {
throw new DomainException(
pht(
'Attempt to write to undeclared property %s::%s.',
get_class($this),
$name));
}
public function current() {
$this->throwOnAttemptedIteration();
}
public function key() {
$this->throwOnAttemptedIteration();
}
public function next() {
$this->throwOnAttemptedIteration();
}
public function rewind() {
$this->throwOnAttemptedIteration();
}
public function valid() {
$this->throwOnAttemptedIteration();
}
private function throwOnAttemptedIteration() {
throw new DomainException(
pht(
'Attempting to iterate an object (of class %s) which is not '.
'iterable.',
get_class($this)));
}
}