eval { fQ_moofancy->new } or say $@;

my $foo = fQ_moonimal->new(size => 3);
my $fooncy = fQ_moofancy->new(3);
my $fixed = fQ_FIXED->new(3);
for ( 1 .. 5 )
{
    say "   foo -> $foo";
    say "fooncy -> $fooncy";
    say " fixed -> $fixed";
    $foo->push($_);
    $fooncy->push($_);
    $fixed->push($_);
}
__END__
isa check for "size" failed: size must be a positive integer at…

   foo -> 
fooncy -> 
 fixed -> _ _ _
   foo -> 1
fooncy -> 1
 fixed -> _ _ 1
   foo -> 1 2
fooncy -> 1 2
 fixed -> _ 1 2
   foo -> 1 2 3
fooncy -> 1 2 3
 fixed -> 1 2 3
   foo -> 1 2 3
fooncy -> 2 3 4
 fixed -> 2 3 4