$ 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.