Aerys\Router::boot PHP Method

    public function boot(Server $server, PsrLogger $logger)
    {
        $server->attach($this);
        $this->bootLoader = static function (Bootable $bootable) use($server, $logger) {
            $booted = $bootable->boot($server, $logger);
            if ($booted !== null && !$booted instanceof Middleware && !is_callable($booted)) {
                throw new \InvalidArgumentException("Any return value of " . get_class($bootable) . '::boot() must return an instance of Aerys\\Middleware and/or be callable');
            }
            return $booted ?? $bootable;
        };
    }