Win8 Strawberry 5.8.9.5 (32)  Sun 11/22/2020  3:11:34
C:\@Work\Perl\monks
>perl -l
use strict;
use warnings;

BEGIN {
    my %ops = (
        ADD_DATA    => [ qw(add    1) ],
        REMOVE_DATA => [ qw(remove 2) ],
        );
    sub valid (*) { return exists $ops{$_[0]}; }
    sub modes (*) {
        return valid($_[0]) ? [ @{ $ops{$_[0]} } ] : die "bad '$_[0]'";
        }
    }

print 42    + modes(ADD_DATA)     ->[1];
print 'foo' . modes('REMOVE_DATA')->[0];

print 'invalid' if not valid(yyy);
print modes('xxx');
^Z
43
fooremove
invalid
bad 'xxx' at - line 11.