I think if prodigal_erik is worried about autovivification then perhaps locking the keys might be a good idea?... use 5.016; use warnings; use Hash::Util

I think if prodigal_erik is worried about autovivification then perhaps locking the keys might be a good idea?... use 5.016; use warnings; use Hash::Util 'lock_keys'; my %a = (B => 100); # B but no A defined lock_keys %a; my $x = 'A'; ++$a{$x}; Above now throws an error on the last line - Attempt to access disallowed key 'A' in a restricted hash... Alternatively autovivification can be switched off - https://metacpan.org/pod/autovivification https://metacpan.org/pod/autovivification