class_has 'db'   => (is => 'rw',isa => 'Str', default => 'theDB');
class_has 'port' => (is => 'rw',isa => 'Int', default => 3306);
class_has 'host' => (is => 'rw',isa => 'Str', default => '127.0.0.1');
class_has 'user' => (is => 'rw',isa => 'Str', default => 'theUSER');
class_has 'pwd'  => ( s => 'rw',isa => 'Str', default => 'thePASS');

sub dbh {
  my $self = shift;
  my $dsn = 'DBI:mysql:' . GSM::SQLConnection->db .
            ';host=' . GSM::SQLConnection->host . 
            ';port=' . GSM::SQLConnection->port;
  return DBI->connect_cached( $dsn, 
    GSM::SQLConnection->user, 
    GSM::SQLConnection->pwd
  );
}

no Moose;
no MooseX::ClassAttribute;
__PACKAGE__->meta()->make_immutable();

...

 my $sth = SQLConnection->dbh()->prepare( ... )