Polymorphism in Elixir

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I didn’t have room for this in my book

This topic is explored in more depth in my book

These two statements contradict each other, perhaps the footer on the blog is generic and doesn’t apply in this case?

I think behaviours also deserve a mention along with protocols. My experience is that it’s quite rare to write a protocol, compared to a behaviour.

For example, Eq could also be implemented using a behaviour:

defmodule Eq do
  @callback eq?(a :: struct, b :: map) :: boolean

  def eq?(%type{} = a, b) do
    type.eq?(a, b)
  end
end

defmodule Cat do
  defstruct [:name, :microchip]

  @behaviour Eq

  def eq?(%Cat{microchip: a}, %{microchip: b}), do: a == b
end

iex(1)> Eq.eq?(%Cat{microchip: "foo"}, %{microchip: "foo"})
true
iex(2)> Eq.eq?(%Cat{microchip: "foo"}, %{microchip: "bar"})
false
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