$ perl
*ro = \'readonly_dynamic';

print "=$ro=\n";
defined eval {$ro = 'newval'}
  or print "Exception: $@";
^D
=readonly_dynamic=
Exception: Modification of a read-only value attempted at - line 4.

##</code><code>##

$ perl
use Lexical::Alias;
# 5.8+, see pod

my $ro;
alias ${\'readonly_lexical'}, $ro;

print "=$ro=\n";
defined eval {$ro = 'newval'}
  or print "Exception: $@";
^D
=readonly_lexical=
Exception: Modification of a read-only value attempted at - line 8.

##</code><code>##

$ perl
use Array::RefElem qw/av_store hv_store/;

hv_store %h, 'ro', ${\'readonly_hashval'};
av_store @a, 5, ${\'readonly_aryelem'};

print "=$h{ro}=$a[5]=\n";
defined eval {$h{ro} = 'newval'}
  or print "Exception: $@";
defined eval {$a[5] = 'newval'}
  or print "Exception: $@";

^D
=readonly_hashval=readonly_aryelem=
Exception: Modification of a read-only value attempted at - line 7.
Exception: Modification of a read-only value attempted at - line 9.