Wordpress OOP

custom-oop-wp.php

namespace Wpse240042\Type;

use WP_Post;

interface Book {

    /**
     * @return string
     */
    public function title();

    /**
     * @return string
     */
    public function publisher();

    /**
     * @return int
     */
    public function year();
}

class WpPostBook implements Book {

    /**
     * @var WP_Post
     */
    private $post;

    /**
     * @param WP_Post $post
     */
    public function __construct( WP_Post $post ) {

        $this->post = $post;
    }

    /**
     * @return string
     */
    public function title() {

        return $this->post->post_title;
    }

    /**
     * @return string
     */
    public function publisher() {

        return get_post_meta( $this->post->ID, '_book_publisher', TRUE );
    }

    /**
     * @return int
     */
    public function year() {

        return get_post_meta( $this->post->ID, '_book_publisher', TRUE );
    }
}