Often people will ask how to follow these principles in the world of I/O. The answer is incredibly simple: with values. Return a DTO that encapsulates all the

Often people will ask how to follow these principles in the world of I/O. The answer is incredibly simple: with values. Return a DTO that encapsulates all the business information about the result state of the I/O call. Do not throw exceptions. Log them if you like, but you must return all the data necessary for the business logic to react to failure conditions, encoded in your own use case specific structure. If you don't care about whether you failed due to timeouts or refused connections or query parse failures what have you, don't return that data, just return a hasError kind of property on the return structure (bonus points if your language supports discriminated unions, but this is not necessary). If the parent logic needs to react to timeouts and failures to connect differently, then catch those exceptions or state separately and return didTimeout or cantConnect flags separately. Values values values