laravel 中 collection.php 的部分实现，例如..使用 IteratorAggregate, Countable 接口

iterator.php

<?php

class Library implements IteratorAggregate, Countable
{
    protected $books;

    public function __construct(array $books)
    {
        $this->books = $books;
    }

    public function getIterator()
    {
        return new ArrayIterator($this->books);
    }

    public function count()
    {
        return count($this->books);
    }
}

class Book
{
    public $title;

    public function __construct($title)
    {
        $this->title = $title;
    }
}

$books[] = new Book('Book One');
$books[] = new Book('Book Two');
$books[] = new Book('Book Three');
$lib = new Library($books);

foreach ($lib as $book) {
    echo $book->title . PHP_EOL;
}

echo $lib->count($books);