Thanks a lot for pointing me in the right direction...
I am currently using 5.6.1 but will most certainly upgrade to 5.8.x.
So the only way of enforcing that behavior for hashes will be to require 5.8.0; in my modules?
That will prevent users with older perl from using it...
Yes, I think you're right. On the other hand, you haven't explained
why you rejected the low-tech alternative of using a tied
hash. If it was for speed reasons, and compatibility is important to you, you could fall back to a tied hash implementation on older perls.
Then at least it would work on 5.6.1, albeit slightly
more slowly.