Let’s say I have a behaviour MyBehaviour and a function that may return any module implementing that behaviour. Is it possible to write a type spec for that?

For example (pseudo-code):

defmodule MyBehaviour do
  @callback say_hello() :: String.t()
end

defmodule MyBehaviourImplA do
  @behaviour MyBehaviour
  def say_hello(), do: "Hello from A"
end

defmodule MyBehaviourImplB do
  @behaviour MyBehaviour
  def say_hello(), do: "Hello from B"
end

defmodule ThisIsWhereTheQuestionComesIn do
  @spec get_module_implementing_behaviour() :: ?????
  def get_module_implementing_behaviour(), do: MyBehaviourImplA
end

I want to specify that ThisIsWhereTheQuestionComesIn.get_module_implementing_behaviour/0 could return either MyBehaviourImplA or MyBehaviourImplB (or indeed any module that implements that behaviour).

My use case is for a configurable adapter pattern; I want to write a function that returns whatever the currently configured adapter is.

Thanks as always!