I agree about encapsulation, thats why I mentioned Tie::Hash after demonstrating the raw mechanics in a REPL.

If tied or functional or OO or whatever interface... YMMV! :)

Anyway we are again speculating about the OPs real intention, he just showed us enough to think it's pointless for most thinkable motivations.

So pointless that Perl could/should warn about using literal arrays or hashes as keys...

update

tl;dr ...

I just used a reverse in my example to avoid triviality with a minimal amount of code, it was a workaround not a goal.

The general problem is to use complex data-structures as keys, see also Using hashes for set operations... for a similar discussion.