code: func S3AllKeysArnForBucket(bucket interface{}) *gocf.StringExpr {
  	arnParts := []gocf.Stringable{
  		gocf.String("arn:aws:s3:::"),
  		DynamicValueToStringExpr(bucket),
  		gocf.String("/*"),
  	}
  	return gocf.Join("", arnParts...).String()
  }
docs: // S3AllKeysArnForBucket returns a CloudFormation-compatible Arn expression
  // (string or Ref) for all bucket keys (`/*`).  The bucket
  // parameter may be either a string or an interface{} ("Ref: "myResource")
  // value