I am not really an expert on Moose but here is one attempt:

package FixedSizeQueue;
use Moose;

has "max_size" => (is => "ro", isa => "Int", default => 10);
has "items" => (is => "ro", isa => "ArrayRef", default => sub { [] });

sub pop {
 my($this)=@_;

 pop @{$this->items};
}

sub push {
 my($this, $item)=@_;

 push @{$this->items}, $item;
 shift @{$this->items} if scalar @{$this->items} > $this->max_size;
}
[download]

This is fuctional but you need to be intantiate it like this:

my $q = FixedSizeQueue->new(max_size => 3);
$q->push(3);
$q->push(5);
$q->push(7);
$q->push(9);
print Dumper($q);
[download]

If you want to supply only an integer to the constructor you need to add a BUILDARGS-method to the above:

sub BUILDARGS {
  my($this, $max_size)=@_;

  return { max_size => $max_size };
}
[download]

Now you can use it like your Ruby-example:

my $q = FixedSizeQueue->new(3);
$q->push(3);
$q->push(5);
$q->push(7);
$q->push(9);
print Dumper($q);
[download]

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