hidden_keys

List the “hidden” placeholder keys of a restricted hash — legal keys that currently have no value assigned.

Synopsis

my @hidden = hidden_keys(%hash);

A hidden key is one that is allowed by the hash’s keyset but fails both exists and defined — typically the ghost left behind after a delete on a locked hash, or a key reserved in advance by lock_keys_plus. Assigning to a hidden key brings it into the visible keyset.

Returns the empty list on an unrestricted hash. The feature is experimental and closely tied to the current restricted-hash implementation; do not build durable contracts on top of it.