Normaly, PHP Object can have property freely. But I want to force Object to have the property. This implementation make it possible.

ForceProperty.php

<?php

class ForceProperty {
	private $val;
	
	public function __get($name) {
		if (property_exists($this, $name)) {
			return $this->$name;
		} else {
			throw new LogicException(sprintf('Undefined property: $%s', $name));
		}
	}
	
	public function __set($name, $value) {
		if (property_exists($this, $name)) {
			$this->$name = $value;
		} else {
			throw new LogicException(sprintf('Undefined property: $%s', $name));
		}
	}
}

$fp = new ForceProperty();
$fp->val = "foo";
$fp->undefined = "var"; // => LogicException: Undefined property: $undefined
echo $fp->val; // => foo