Core/src/ServiceBuilder.php
private function createClient($class, $packageName, array $config = [])
    {
        if (class_exists($class)) {
            return new $class($this->resolveConfig($config + $this->config));
        }
        throw new \Exception(sprintf(
            'The google/cloud-%s package is missing and must be installed.',
            $packageName
        ));
    }
private function createClient($class, $packageName, array $config = [])
    {
        if (class_exists($class)) {
            return new $class($this->resolveConfig($config + $this->config));
        }
        throw new \Exception(sprintf(
            'The google/cloud-%s package is missing and must be installed.',
            $packageName
        ));
    }
private function createClient ( $ class , $ packageName , array $ config = [ ] ) { if ( class_exists ( $ class ) ) { return new $ class ( $ this -> resolveConfig ( $ config + $ this -> config ) ) ; } throw new \ Exception ( sprintf ( 'The google/cloud-%s package is missing and must be installed.' , $ packageName ) ) ; }
Create the client library, or error if not installed.

@param string $class The class to create.
@param string $packageName The name of the package
@param array $config Configuration options.
Create the client library or error if not installed .