lstor

defmodule Crypto do
  def md5(data) do
    :erlang.md5(data)
    |> :erlang.bitstring_to_list
    |> Enum.map(&(:io_lib.format("~2.16.0b", [&1])))
    |> List.flatten
    |> :erlang.list_to_bitstring
  end
end

timruffles

In many production systems you'll want to have one module capable of talking to many potential implementations of a collaborator module (e.g a in memory cache, a redis-based cache etc). While testing it's useful to control which module the module under test is talking to.

Here are the approaches I can see. The two points that seem to divide the approaches are their tool-ability (dialyzer) and their ability to handle stateful implementations (which need a pid).

Passing modules

Modules are first class, so you can pass them in. Used in EEx, where passed module must implement a behaviour.