has '_posts' => (is => 'ro', lazy => 1, traits => ['Hash'], isa => 'HashRef[HashRef]', builder => '_load_posts',                                
                handles => { set_post => 'set', get_post => 'get', num_posts => 'count',                                                       
                post_pairs => 'kv', post_keys => 'keys' }, writer => '_set_posts');
##</code><code>##

use Storable;
store { {} }, $file;  # This line needs to be changed.
...
$s->_set_posts(retrieve $file);

##</code><code>##

Attribute (_posts) does not pass the type constraint because: Validation failed for 'HashRef[HashRef]' with value 1 at native delegation method Site::Posts::num_posts (count) of attribute _posts

##</code><code>##


package Site::Posts ;

use Moose;
use Storable;
use Data::Dumper qw(Dumper);
use namespace::autoclean;

has '_posts' => (is => 'ro', lazy => 1, traits => ['Hash'], isa => 'HashRef[HashRef]', builder => '_load_posts',
                handles => { set_post => 'set', get_post => 'get', num_posts => 'count',
                post_pairs => 'kv', post_keys => 'keys' }, writer => '_set_posts');
has 'file'   => (is => 'ro', isa => 'Str', required => 1 );



### Public methods ###

sub list {
  my $s = shift;

  if ($s->num_posts) { 
    my @keys = $s->post_keys;
    print Dumper \@keys;
  }
}


sub add {
  my $s = shift;
  my $id = shift;

  $s->set_post($id => {exists => 1});
}

sub delete {
  my $s = shift;
  store { {} }, $s->file;
}

sub save {
  my $s = shift;
  store $s->_posts, $s->file;
}


### Private methods ###
sub _load_posts {                                                                                                                               
  my $s = shift;                                                                                                                                
                                                                                                                                                
  if ( !-f $s->file ) {                                                                                                                                                                                                                                                
    store { {} }, $s->file;                                                                                                                     
  }                                                                                                                                             
  my $posts = retrieve $s->file;                                                                                                                
  $s->_set_posts($posts);                                                                                                                       
}                                                                                                                                               


1;