add-shortcodes.php

<?php
$shortcodes = [
  'recent_posts' => __DIR__ . 'views/recent-posts.php',
  'products' => __DIR__ . 'views/products.php'
];

new Shortcodes( $shortcodes );

basic-posts-class.php

<?php
class Posts {
	
	/**
	* @var \WP_Query
	*/
	protected $query;
	
	public function __construct( array $args )
	{
		$this->query = new \WP_Query( $args );
	}

	public function getQuery() : \WP_Query
	{
		return $this->query;
	}

	public function getPosts() : array
	{
		return $this->query->posts;
	}
}

dynamic-shortcodes.php

class Shortcodes {

	/**
	 * Shortcode collection
	 *
	 * @var array
	 */
	protected $shortcodes;

	/**
	 * Shortcodes constructor.
	 *
	 * @param array $shortcodes Shortocdes to use in form of 'tag' => 'template_path'
	 */
	public function __construct( array  $shortcodes )
	{
		$this->shortcodes = $shortcodes;
		foreach ( $shortcodes as $shortcode => $template ){
			if( is_file( $template ) && file_exists( $template ) ){
				add_shortcode( $shortcode, [ $this, $shortcode ] );
			}

		}
	}

	/**
	 * Dynamically create callback for shortcodes
	 *
	 * @param string $name The shortcode tag
	 * @param array $arguments Not used right now, but could be used for shortcode atts
	 *
	 * @return string
	 */
	public function __call( $name, $arguments )
	{
		if( array_key_exists( $name, $this->shortcodes ) ){
			return $this->genericHandler( $this->toCamelCase( $name ), $this->shortcodes[ $name ] );
		}
	}

	/**
	 * Render a shortcode using posts collection and its corresponding post collection
	 *
	 * @param string $collection_name
	 * @param string $template
	 *
	 * @return string
	 */
	protected function genericHandler( string $collection_name, string $template )
	{
		$posts = System::getInstance()->getContainer()->get( $collection_name )->getPosts();
		ob_start();
		include $template;
		return ob_get_clean();
	}

	/**
	 * Turn shortcode name into camelCased argument
	 *
	 * @param $string
	 *
	 * @return string
	 */
	protected function toCamelCase($string) : string
	{
		$string = str_replace('-', ' ', $string);
		$string = str_replace('_', ' ', $string);
		$string = ucwords(strtolower($string));
		$string = str_replace(' ', '', $string);
		return $string;
	}
}

install-di.sh

composer require php-di/php-di
composer require ocramius/proxy-manager

post-collections.php

<?php
class PostCollections {

	protected static $recent_posts;

	protected static  $products;

	public function recent_posts() : array
	{
		if( null === static::$recent_posts ){
			static::$recent_posts = ( new Posts( [ 'posts_per_page' => 3 ] ) )->getPosts();
		}

		return static::$recent_posts;
	}


	public function products() : array
	{
		if( null === static::$products ){
			static::$products = ( new Posts( [ 'posts_per_page' => 15, 'post_type' => 'product' ] ) )->getPosts();
		}

		return static::$products;
	}
	
}

PostsFactory.php

<?php

class PostsFactory {

	public static function create( $post_type, int $posts_per_page = 10, int $page = 1, array  $args = [] ) : Posts
	{
		$args = wp_parse_args(  $args, [
			'post_type' => $post_type,
			'posts_per_page' => $posts_per_page,
			'page' => $page
		] );
		return new Posts( $args );
	}
}

router-example.php

<?php

add_action( 'plugins_loaded', function(){

	add_action( 'parse_request', function( \WP $wp ){
		if( isset( $wp->query_vars[ 'name' ] ) ){
			switch( $wp->query_vars[ 'name' ] ){
				case 'recent-posts' :
					$route = 'RecentPosts';
					break;
				case 'products' :
					$route = 'Products';
				break;
				default:
					$route = null;
				break;
			}

			if( $route ){
				status_header( 200 );
				$controller =  new Controller();
				echo $controller->$route( System::getInstance()->getContainer()->get( $route ) );
				exit;
			}
		}
	});


});


class Controller {


	public function recentPosts( Posts $posts )
	{

		$posts = $posts->getPosts();

	}

	public function prodcuts( Posts $posts )
	{
		$posts = $posts->getPosts();
	}

}

shortcode-di

<?php
class RecentPostShortcode {
	protected $posts;

	protected $template_path;

	const SHORTCODE_NAME = 'recent_posts_shortcode';

	public function __construct( array $posts, string $template_path )
	{
		$this->posts = $posts;
		$this->template_path = $template_path;
	}

	public function handler(){
		ob_start();
		$posts = $this->posts;
		include  $this->template_path;
		return ob_get_clean();
	}


}

add_action( 'init', function(){
	$object = new RecentPostShortcode( PostsFactory::create( 'post', 3 ), '/path/to/template.php' );
	add_shortcode( RecentPostShortcode::SHORTCODE_NAME, [ $object, 'handler' ] );
});

shortcode-no-di.php

class recent_posts_shortcode{

	/**
	 * @var \WP_Query
	 */
	protected $query;

	public function __construct() {
		add_shortcode( 'recent_posts', [ $this, 'handler' ] );
	}

	public function handler(){
		$this->do_query();
		while( $this->query->have_posts()  ){
			$this->query->the_post();
			echo $this->query->post->post_title;
		}
	}

	protected function do_query(){
		$this->query = new \WP_Query( [
			'post_type' => 'posts',
			'posts_per_page' => 3
		] );
	}

}

add_action( 'init', function(){
	$class = new recent_posts_shortcode();
});

System.php

use DI\ContainerBuilder;

final class System {
	/**
	 * @var \DI\Container
	 */
	protected $container;

	/**
	 * @var System
	 */
	protected static $instance;

	protected function __construct() {
		$this->buildContainer();
	}

	public function getInstance() : System
	{
		if( null == static::$instance ){
			static::$instance = new static();
		}

		return static::$instance;
	}

	
	public function getContainer() :  \DI\Container
	{
		return $this->container;
	}

	/**
	 * @return \DI\Container
	 */
	protected function buildContainer() {
		$builder = new ContainerBuilder();
		$builder->addDefinitions( [
			'RecentPosts' => function ( ContainerBuilder $c ) {
				return PostsFactory::create( 'post', 3 );
			},
			'Products'   => function ( ContainerBuilder $c ) {
				return PostsFactory::create( 'product', 50 );
			}
		] );

		$this->container = $builder->build();

	}

}

wp-god-singleton-example.php

<?php
/*
Plugin Name: Example of the God Singleton
*/

final class Plugin {
  
  public $emails;
  
  public $settings;
  
  public $database;
  
  public $api;
  
  public $admin;
  
  public $front_end;
  
  public $assets;
  
  protected static $instance;
  
  private function __construct(){}
  
  public function get_instance(){
    if( null === self::$instance ) {
      self::$instance = new self();
      self::$instance->emails = new Plugin_Emails();
      self::$instance->settings = new Plugin_Setttings();
      self::$instance->database = new Plugin_Database();
      self::$insanct->api = new Plugin_Api();
      self::$instance->front_end = new Plugin_Front_End();
      self::$instance->assets = new Plugin_Assets();
      
    }
    
    return self::$instance;
    
  }
  
}

add_action( 'init', array( 'Plugin', 'get_instance' ) );