Form.php

<?php

namespace DesignPatterns\Structural\Composite;

/**
 * The composite node MUST extend the component contract. This is mandatory for building
 * a tree of components.
 */
class Form extends FormElement
{
    /**
     * @var array|FormElement[]
     */
    protected $elements;

    /**
     * runs through all elements and calls render() on them, then returns the complete representation
     * of the form
     *
     * from the outside, one will not see this and the form will act like a single object instance
     *
     * @param int $indent
     *
     * @return string
     */
    public function render($indent = 0)
    {
        $formCode = '';

        foreach ($this->elements as $element) {
            $formCode .= $element->render($indent + 1) . PHP_EOL;
        }

        return $formCode;
    }

    /**
     * @param FormElement $element
     */
    public function addElement(FormElement $element)
    {
        $this->elements[] = $element;
    }
}