Defoverridable disclaimer to use it with care - but why?

Questions & Help Questions
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14

Normally, the implementations are called through the dependency injection and they don’t need any use clause. Like this

defmodule TestBeh do
  @callback ok :: :ok
  @callback ko :: :ko

  @optional_callbacks ko: 0

  @default_impl Application.compile_env(:foo, :test_beh, TestImpl)

  # default implementation
  def ko, do: :ko

  def ok(impl \\ @default_impl), do: impl.ok()
  def ko(impl \\ @default_impl) do
    impl = if function_exported(impl, :ko, 0), do: impl, else: __MODULE__
    impl.ko()
  end 
end