required moose attributes

req

#!/usr/bin/perl
use strict;
use feature qw{ say };
use warnings;

{   package My;
    use Moose;

    my $m = 1;

    has req =>  ( is => 'ro', default => sub { $m }, required => 1, predicate => 'has_req' );
    has nreq => ( is => 'ro', default => sub { $m }, required => 0, predicate => 'has_nreq' );
    has laz =>  ( is => 'ro', default => sub { $m }, lazy => 1, predicate => 'has_laz' );
    has buil => ( is => 'ro', required => 1, lazy => 1, builder => 'get_m', predicate => 'has_buil' );

    sub get_m { $m }
    sub inc { $m++ }

    no Moose;
    'My'->meta->make_immutable;
}

my $o = 'My'->new;
my $m;
$m = "has_$_", say "$m ", $o->$m for qw( req nreq laz buil );
$o->inc;
say "$_ ", $o->$_ for qw( req nreq laz buil );
$m = "has_$_", say "$m ", $o->$m for qw( req nreq laz buil );