sub serialise {
    my( $self, $format ) = @_;
    if( $format eq 'Storable' ) {
        require Storable;
        return freeze $self;
    } 
    elsif( $format eq 'Data::Dumper' ) {
        require Data::Dumper;
        return dump $self;
        
    }
    elsif( ... ) {
    	
    }
    ...
    else {
    	die "Unknown serialisation format: $format";
    }
}

## Equivalent code for deserialisation.