<?php

class User {}
class UserReduced {
    public function __construct(User $user) {
        $this->user = $user;
    }
}
class CustomUserCollection extends ArrayObject {
    public function __construct($input = [], $flags = 0, $iteratorClass = 'ArrayIterator') {
        // magic
        $input = array_map(function ($user) {
            return new UserReduced($user);
        }, $input);

        parent::__construct($input, $flags, $iteratorClass);
    }
}

$users = [];
for ($i = 0; $i < 10; ++$i) {
    $users[] = new User();
}

// Case
$userReduces = iterator_to_array(new CustomUserCollection($users));