I'm trying to create a read-only "multi-dimensional" constant using the built-in constant pragma. I know that there's the Readonly module (amongst others), but I'm trying to stick to basics.

Using anonymous list references doesn't really work, because they can be modified, as documented:

Even though a reference may be declared as a constant, the reference may point to data which may be changed, as this code shows.

use constant ARRAY => [ 1,2,3,4 ];
print ARRAY->[1];
ARRAY->[1] = " be changed";
print ARRAY->[1];
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Okay, so I'll use some sort of indirection, I thought, and came up with something like this:

use strict;
use warnings;
use Data::Dumper;

use constant INVALID_DATA => ( q{invalid}, 0 );
use constant ADD_DATA => ( q{add}, 1 );
use constant REMOVE_DATA => ( q{remove}, 2 );
use constant MODES => ( \&ADD_DATA, \&REMOVE_DATA );

print {*STDERR} "Dumping MODES: " . Dumper ((MODES));

1;
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… but, this doesn't quite do what I expected. Output:

Dumping MODES: $VAR1 = sub { "DUMMY" };
$VAR2 = sub { "DUMMY" };
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I was under the impression that constants are really subs that I could take the reference of, but this doesn't seem to be the case.

Alternatively, I've tried taking direct references, but this is... just merging the lists (which is obviously bad to begin with and what I wanted to avoid by using references) in a weird "reference all elements individually" way:

use constant MODES => ( \ADD_DATA, \REMOVE_DATA );
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leading to

Dumping MODES: $VAR1 = \'add';
$VAR2 = \1;
$VAR3 = \'remove';
$VAR4 = \2;
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Is there any proper way to do this?