Failure modes/types

[taylorthurlow]

Similar to collectiveidea/interactor#165, it might be nice to support a way to fail an interaktor with a particular type. It could be that the desire for multiple failure types is a symptom of having interaktors which are too complicated, but I'm leaning towards that not necessarily being true. If this were to be implemented I could see a new symbol argument being added to #fail! which represents the failure mode.

Take for example an interaktor which is invoked when a web request is received by an API. The interaktor is designed to create a new record in a database. That record may fail validation, or perhaps the record already exists. Typically error handling would be different between these two cases - maybe the API endpoint wants to send the right HTTP response code.

fail!(:validation, errors: record.errors)

fail!(:duplication, error: "The record already exists.")

It could also be useful to define these failure modes on the interaktor definition:

failure_mode :validation, :duplication

This would also aid in generating methods to check the error type, like #validation_error? or #duplication_error? in the example above. If they are defined, then specifying one when calling #fail! would be required.