How to return "type conforming to Behaviour" in function spec?

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1

Hi folks,

I want to create a function spec which tells the compiler that the return type will be conforming to a given Behavior. This question was asked several times many years ago, here and e.g. on StackOverflow: elixir - How to use typespecs and Dialyzer with Behaviours? - Stack Overflow

I am re-asking (with the exact same title as SO) as I want to get reassurance whether this problem is now solved with dialyzer nowadays. Back then at SO, this returned a dialyzer error:

  @spec greeter() :: GreeterBehaviour # This doesn't work with dialyzer
  def greeter do
    FormalGreeter # Can easily be swapped to CasualGreeter
  end

# lib/my_app.ex:19: Invalid type specification for function 'Elixir.MyApp':greeter/0. The success typing is () -> 'Elixir.FormalGreeter'

Nowadays, using Elixir 1.18.2 and dialyzer 1.4.3, I don’t get such error message, is this problem solved nowadays - while there is no error message thrown, I don’t get type inference in LSP, thus my question. I am unsure whether this spec literally returns the GreeterBehaviour module or "a module conforming to GreeterBehaviour.
Thanks!

2

The term GreeterBehaviour is an atom; using it in a typespec’s return value position means “this function will return this specific atom”.

1 Like
3

ok, this is not what I want.
So there is still no way to specify a generic return type which conforms to a given Behaviour?