Isn't a language extension for a rather rare use case kind of overenineered? Wouldn't a read-only reference be sufficient and at the same time more flexible and better readable? Explicitly creating a read-only reference is clearly visible and lets you choose any name.

Readonly has the clumsy named sub Scalar1. Just rename it.

#!/usr/bin/perl

use v5.14;
use warnings;
use Readonly ();

BEGIN {
    *ro_ref = \&Readonly::Scalar1;
}

my @arr = (2, 3, 4);
ro_ref my $arr, \@arr;

@arr = (3, 4, 5);
say "@$arr";
eval {$arr = [4, 5, 6]; 1} || warn $@;

__DATA__
Modification of a read-only value attempted at /home/jo/Programs/play-
+scripts/ro-ref.pl line 16.
3 4 5
[download]