elixir-protocol-derive-example.ex

defprotocol P do
  def x(p)
end

defimpl P, for: Integer do
  def x(p) do
    p + 1
  end
end

defimpl P, for: M do
end

defimpl P, for: Any do
  def x(p) do
    p
  end
end

defmodule M do
  @derive [P]
  defstruct [:a]
end

P.x 2 # => 3
P.x "a" # => Error Not implemetned for string
P.x %M{} # => %M{}