Composite pattern is intended to compose objects into tree structures to represent whole-part hierarchies. Composite lets clients treat individual objects and compositions of objects uniformly. Use this pattern whenever you have composites that contain components, each of which could be a composite. The whole point of the Composite pattern is that the Composite can be treated atomically, just like a leaf. At the heart of this pattern is the ability for a client to perform operations on an object without needing to know that there are many objects inside.

Example
In this example, the OneBook class is the individual object. The BooksSet class is a group of zero or more OneBook objects. Both the OneBook and BooksSet can return information about the books title and author. OneBook can only return this information about one single book, while BooksSet will return this information one at a time about as many OneBooks as it holds. 

interface IBook {
    function getBookInfo();
}

class OneBook implements IBook {
    private $title;
    private $author;
    function __construct($title, $author) {
        $this->title = $title;
        $this->author = $author;
    }
    function getBookInfo() {
        echo $this->title." by ".$this->author . "<br>";
    }
}

class BooksSet implements IBook {
    private $oneBooks = [];
    public function getBookCount() {
        return count($this->oneBooks);
    }
    public function getBookInfo() {  
        foreach ($this->oneBooks as $book) {
            echo $book->getBookInfo();
        }
    }
    public function addBook($oneBook) {
        $this->oneBooks[] = $oneBook;
        return $this->getBookCount();
    }
    public function removeBook($oneBook) {
        $index = array_search($oneBook, $this->oneBooks);
        unset($this->oneBooks[$index]);
        return $this->getBookCount();
    }
}

$firstBook = new OneBook('Core PHP Programming, Third Edition', 'Atkinson and Suraski');
$secondBook = new OneBook('PHP Bible', 'Converse and Park');
$thirdBook = new OneBook('Design Patterns', 'Gamma, Helm, Johnson, and Vlissides');

$firstBook->getBookInfo();
echo "<hr>";

$firstBooksSet = new BooksSet();
$firstBooksSet->addBook($firstBook);
$firstBooksSet->addBook($secondBook);

$secondBooksSet = new BooksSet();
$secondBooksSet->addBook($thirdBook);
$secondBooksSet->addBook($firstBooksSet);
$secondBooksSet->getBookInfo();
echo "<hr>";
$secondBooksSet->removeBook($thirdBook);
$secondBooksSet->getBookInfo();


Result of the example:

Core PHP Programming, Third Edition by Atkinson and Suraski

Design Patterns by Gamma, Helm, Johnson, and Vlissides
Core PHP Programming, Third Edition by Atkinson and Suraski
PHP Bible by Converse and Park

Core PHP Programming, Third Edition by Atkinson and Suraski
PHP Bible by Converse and Park

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#php #design_patterns