public function getConcrete()
    {
        if ($this->instance) {
            return $this->instance;
        }

        if (is_object($this->concrete) || $this->concrete instanceof Closure) {
            $instance = $this->concrete;
        } else {
            $instance = $this->context->getContainer()->make($this->concrete);
        }

        if (! $this->isDynamic()) {
            $this->checkConcreteInstance($instance);
        }

        return $this->instance = $instance;
    }