use MooseX::Declare;
...
...
...
    has 'error_log' => (
        is => 'rw',
        isa => 'ArrayRef',
        default => sub { [] }
    );
...
...
...
    method register_error {
        shift;
        my $s_message = shift;
        return unless defined $s_message;
        $self->error_log->push ($s_message);
        return $self->error_log->length;        
    }