code: func (storage *MessageBodyStorage) BucketArn() *gocf.StringExpr {
  	return gocf.Join("",
  		gocf.String("arn:aws:s3:::"),
  		storage.bucketNameExpr)
  }
docs: // BucketArn returns an Arn value that can be used as an
  // lambdaFn.RoleDefinition.Privileges `Resource` value.