sub _copy {
  my $this = shift;
  if (not ref $this) {
    $this
  }
  elsif (ref $this eq "HASH") {
    +{map { $_ => _copy($this->{$_})} keys %$this}
  }
  elsif (ref $this eq "ARRAY") {
    [map _copy($_), @$this]
  }
  elsif (ref $this eq "CODE") {
    # do some processing here, the following is a 
    # placeholder
    'CODEREF'
  }
  else {
    Carp::croak "What's a " . ref $_ . "?" 
  }
}

##</code><code>##

sub _iterative_copy {
  my $this     = shift;
  my @pile     = $this;
  my $this_new = {};
  my $root     = $this_new;
  my @pile_new = $this_new;
  
  while (defined($this = shift @pile)) {
    $this_new = shift @pile_new;
    if (ref $this eq "HASH") {
      for (keys %$this) {
        if (ref (my $v = $this->{$_})) {
          if (ref $v eq "HASH") {
            $this_new->{$_} = {}
          }
          elsif (ref $v eq "ARRAY") {
            $this_new->{$_} = []
          }
          elsif (ref $v eq "CODE") {
            # do some processing here,
            # the following is a placeholder
            $this_new->{$_} = "CODEREF"
          }
          else {
            Carp::croak "What's a " . ref $v
          }
          unshift @pile, $v;
          unshift @pile_new, $this_new->{$_};
        }
        else {
          $this_new->{$_} = $v
        }
      }
    }
    # quietly ignore coderefs,
    # they are dealt with in the inner loop
    elsif (ref $this ne "CODE") {
      Carp::croak "What's a " . ref $this
    }
  }
  
  $root;