<?php
 
class Organisation {
 
	private $name;
	private $departments = [];
 
	public function __construct($name) {
		$this->name = $name;		
	}
 
	public function addDepartment(Department $dep) {
 
		$exist = false;
 
		foreach ($this->$departments as $department) {
			if ($department === $dep) {
				$exist = true;
			}
		}
 
		if ($exist == false) {
			$this->departments[] = $dep;
		}
 
	}
 
 
}
 
class Department {
	public function __construct($name) {
		$this->name = $name;
	}
}
 
$vector = new Organisation('Вектор');
 
$dep1 = new Department('dep1');
$vector->addDepartment($dep1);
$vector->addDepartment($dep1);
 
var_dump($vector);
 

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