code: public function resolve($concrete, array $args = [])
      {
          $instance = $concrete;
  
          if (is_callable($concrete)) {
              //$concrete = $this->resolveCallable($concrete);
              $instance = $this->call($concrete, $args);
          }
  
          if (is_string($concrete) && class_exists($concrete)) {
              //$concrete = $this->resolveClass($concrete);
              $instance = $this->build($concrete, $args);
          }
  
          return $instance;
      }
docs: $concrete c'est un mixed