constMemory(string $fileName);

$config = ['path' => './tests'];
$excel  = new \Vtiful\Kernel\Excel($config);
​
$fileObject = $excel->constMemory('tutorial01.xlsx');
$fileHandle = $fileObject->getHandle();
​
$format    = new \Vtiful\Kernel\Format($fileHandle);
$boldStyle = $format->bold()->toResource();
​
$fileObject->setRow('A1', 10, $boldStyle) // 写入数据前设置行样式
    ->header(['name', 'age'])
    ->data([['viest', 21]])
    ->output();