quickly adding this and MX::Nonmoose::InsideOut to MyMVR:

sub FOREIGNBUILDARGS { return @{$_[2]}}
[download]

@_ is (class, key (vec), and value (arrayref)) from the adjusted script:

use MyMVR;

my $a = MyMVR->new(vec=>[0,0,0]);
my $b = MyMVR->new(vec=>[1,1,1]);

print $_ ."\n" foreach (@{$a - $b});
print $a->dist($b) . "\n";
[download]

which works. Thanks!