Programming Elixir 1.2

Implementing a Protocol

The defimpl macro lets you give Elixir the implementation of a protocol for one or more types. The code that follows is the implementation of the Inspect protocol for PIDs and references.

defimpl Inspect, for: PID do
  def inspect(pid, _opts) do
    "#PID" <> IO.iodata_to_binary(pid_to_list(pid))
  end
end

defimpl Inspect, for: Reference do
  def inspect(ref, _opts) do
    '#Ref' ++ rest = :erlang.ref_to_list(ref)
    "#Reference" <> IO.iodata_to_binary(rest)
  end
end

Finally, the Kernel module implements inspect, which calls Inspect.inspect with its parameter. This means that when you call inspect(self), it becomes a call to Inspect.inspect(self). And because self is a PID, ...