gistfile1.txt

# part of my library
defmodule FooLib do
  defprotocol BarProtocol do
    def bar(value)
  end

  defimpl BarProtocol, for: List do
    def bar([h | _rest]), do: h
  end

  defimpl BarProtocol, for: Tuple do
    def bar({h, _rest}), do: h
  end

  @spec foo(list) :: any
  @spec foo(tuple) :: any
  # how can I define spec for protocol?
  def foo(value) do
    BarProtocol.bar(value)
  end
end

# part of 3rd party library, which implements BarProtocol
defmodule BazStruct do
  defstruct bar: "buzz"
end

defimpl BarProtocol, for: BazStruct do
  def bar(%BazStruct{bar: value}), do: value
end