Glenn Jones

Default arguments in an elixir plug

The init and call construction of plugs give you the ability to provide default arguments. Read more about it here. This is a short explenation of how you can work with that.

defmodule Project.CakeDescriber
  def init(opts) do
    default_opts = %{color: red}
    Map.merge(default_opts, opts)

  def call(conn, opts \\ %{}) do
    color = Map.fetch!(opts, :color)
    taste = Map.fetch!(opts, :taste)
    IO.puts(#{color} and #{taste} cakes are the best!”)


Now if you call:

Project.CakeDescriber, %{taste: fruity}

It will return: “red and fruity cakes are the best!”.

Then, if you call:

Project.CakeDescriber, %{taste: carrot-y, color: purple}

It will return: “purple and carrot-y cakes are the best!”.


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