protected function delete($currency)
    {
        $this->output->write("Deleting {$currency} currency...");

        if (is_string($result = $this->storage->delete($currency))) {
            $this->output->writeln('<error>' . ($result ?: 'Failed') . '</error>');
        }
        else {
            $this->output->writeln("<info>success</info>");
        }
    }