<?php

/**
 * A collection that can contain members.
 *
 * @extends IteratorAggregate<int,Member>
 */
interface Collection extends IteratorAggregate
{
}

/**
 * A member of a collection. Also a collection containing only itself.
 *
 * In the real world, this would contain additional methods.
 */
interface Member extends Collection
{
}

class MemberImpl implements Member
{
    /**
     * @return Iterator<int,Member>
     */
    public function getIterator(): Iterator
    {
        return new ArrayIterator([$this]);
    }
}

class CollectionImpl implements Collection
{
    public function __construct(Member ...$members)
    {
        $this->members = $members;
    }

    /**
     * @return Member
     */
    public function getMember(): Member
    {
        return new MemberImpl();
    }

    /**
     * @return Iterator<int,Member>
     */
    public function getIterator(): Iterator
    {
        return new ArrayIterator($this->members);
    }

    /**
     * @var array<int,Member>
     */
    private $members;
}