package Defaulton;

use Moo;
has foo => is => ro => default => sub { 42 };
my $INST = __PACKAGE__->new;

around new => sub {
    my ($orig, $class, @args) = @_;

    return $INST if $INST and $class eq __PACKAGE__ and !@args;

    return $class->$orig(@args);
};

1;