#! perl -slw
use strict;
use Internals qw[ SetReadOnly ];

use constant BAR => { x => 1 };
SetReadOnly( BAR );
BAR->{y} = 12345; ## Modification of a read-only value attempted ...

use constant BAZ => [ 1, 2, 3, 4, 5, ];
SetReadOnly( BAZ );
push @{ +BAZ }, 1; # Modification of a read-only value attempted ... 

## Unfortunately, these do not produce errors?
++BAR->{x};
++BAZ->[0];

__END__
C:\test>junk7
Modification of a read-only value attempted at C:\test\junk7.pl line 13.