# protected add to set credit
sub setCreditAmount {
    my $closure = shift;
    my $amount  = shift;
    caller(0)->isa(__PACKAGE__) || confess "setCreditAmount is protected";
    &{$closure}( "CREDITAMOUNT", $amount );
}

##</code><code>##

# public method to add to the account
sub addToAccount {
    my $closure   = shift;
    my $addAmount = shift;
    my $amount    = $closure->getCreditAmount() + $addAmount;
    $closure->setCreditAmount($amount);
}