package LockedBox;
use Moose;
use MooseX::StrictConstructor;
use Hash::Util qw[ lock_keys lock_value ];

has bar => ( is => 'ro' );

sub BUILD {
    my $self = shift;
    lock_keys( %$self );
    foreach my $attr ( $self->meta->get_all_attributes ) {
        lock_value( %$self, $attr->name )
    }
}