code: func (d *FSDirectory) CreateOutput(name string, ctx IOContext) (out IndexOutput, err error) {
  	d.EnsureOpen()
  	err = d.ensureCanWrite(name)
  	if err != nil {
  		return nil, err
  	}
  	return newFSIndexOutput(d, name)
  }
docs: /*
  Creates an IndexOutput for the file with the given name.
  */