gistfile1.php

<?php
 
 
/**
 * @property-read DbConnection $db
 * @di $db
 */
class BlaBla1 {
  public function doIt() {
    $this->db->query('SELECT NOW()');
  }
}

class BlaBla2 {
  
  /**
   * @di
   * @var DbConnection
   */
  protected $db;
  
  public function doIt() {
    $this->db->query('SELECT NOW()');
  }
}

<?php
class BlaBla implements DiInjected
{
   public $needs = ['db'];

  /**
   * @di
   * @var DbConnection
   */
   protected $db;

   // declared in interface
   function injectServices($services)
   { 
      foreach ($services as $name => $val) {
         if (isset($this->needs[$name]) $this->$name = $val;
      }
   }

}
?>