ReadonlyX combines the best features of p5-Readonly and p5-Readonly-XS,
and is a drop-in replacement. It creates read-only scalars, arrays, and
hashes. It was created by maintainer of Readonly itself.

The author says: "ReadonlyX is the best of recent versions of Readonly
without the old API and without the speed penalty of tie(...). It's what
I'd like to do with Readonly if resolving bugs in it wouldn't break 16
years of code out there in Darkpan."

WWW: https://metacpan.org/pod/ReadonlyX