<?php
class Foo {
	public $name;
	public $type;
	
	public function __construct($name, $type) {
		$this->name = $name;
		$this->type = $type;
	}
}

$array[] = new Foo('first', 0);

$second = new Foo('second', 0);
$array[] = $second;
$array[] = new Foo('third', 1);
$array[] = new Foo('fourth', 1);

$key = array_search($second, $array, true);

print_r($key);