I’ve been trying to figure out how to handle the authorization layer of a Phoenix app I’m working on which has brought me full circle to something I’ve noticed about the Phoenix defaults since I first started tinkering with it:

The default get! functions in contexts raise an Ecto.NoResultsError which is caught and generally displayed as a 404.

In consideration for authorization, does it make sense to just raise some other sort of exception that’s caught somewhere higher up?

With that said, in reading around, I’m having a hard time understanding how the get! convention meshes with advice about exceptions being “exceptional.” Is a lack of a resource in a repo really exceptional? (And I am not being glib either, this is a serious question). This seems like a case of exception as flow control. Is this observation correct? And if it is, is this an acceptable convention in Elixir?

I found this question on StackOverflow and the accepted answer quotes José but doesn’t seem to provide the source. For reference:

In Elixir, this distinction is rather theoretical, but they matter in some languages like Ruby, where using errors/exceptions for control-flow is expensive because creating the exception object and backtrace is expensive.

Are exceptions as flow-control in Elixir acceptable and, more specifically, do they not incur the same sort of performance hit as Ruby?

Asking specifically since I used throw/catch quite a lot in Ruby. In this situation, I’m debating between some sort of :error/:ok pattern or just raising an exception.