Elixir in Action Application structure is wrong

[sasajuric]

@Fl4m3Ph03n1x

Ahh, yes, that is correct. I am merely trying to build on the shoulders of titans

Sure, go ahead, just don’t credit me with your own work

@Fl4m3Ph03n1x

This is where I have trouble understanding the issue. If Todo.System.start_link returns the type Supervisor.on_start , then your Todo.Application.start , which returns whatever Todo.System.start_link returns, should return the same.

The error should still be there, as Todo.System.start_link can in theory still return :ignore , thus causing the signature to be different. Am I miss interpreting something?

The return value of the start callback is a subset of possible return values of Supervisor.start_link. As long as Supervisor.start_link returns that subset, everything is fine. Otherwise, the app will fail to start with an error returned a bad value: :ignore.

Keep in mind that dialyzer can’t detect all possible errors. In fact, in my informal estimate, I feel that dialyzer mostly doesn’t catch errors. In this particular example, I’m pretty sure it would miss the case where :ignore is returned, since that situation is triggered by another process (the supervisor process, if our supervisor callback returns :ignore from it’s init).

If everything was running in the same process, the dialyzer would maybe catch a situation where the called function returns a value which is not allowed by the spec.