test.php

<?php declare(strict_types=1);

class MyData implements IteratorAggregate {

    public $property1;
    public $property2;
    public $property3;

    public function __construct() {
        $this->property1 = new C();
        $this->property2 = new D();
        $this->property3 = new C();
    }

    public function getIterator() {
        return new ArrayIterator($this);
    }
    
    public function anotherMethod() {
        
    }
}

interface I {
    function bar();
}

class C implements I {
    function bar() {}
}

class D implements I {
    function bar() {}
}

$obj = new MyData;

foreach($obj as $key => $value) {
    var_dump($key, $value);
    echo "\n";
}

foo($obj);

/**
 * @param  MyData<I> $data
 */
function foo($data) {
    foreach ($data as $d) {
        $d->bar();
    }
    $data->anotherMethod();
}