Example of Elixir Compilation Dependencies

a.ex

defmodule A do
  @moduledoc """
  # Run yourself my doing a `mix new example` and then copying these files in a.ex, b.ex, c.ex, c2.ex
  # Start - show incremental compile works
    * mix compile

  # Add `elixirc_options: [verbose: true],` to mix.exs
    * mix compile

  # Change A, recompile
    * mix compile

  # Change B, Ask what folks think will happen
    * mix compile

  # Change C, Ask what folks think will happen
    * :mind-blown:
    * mix compile

  # Change C2, Ask what folks think will happen
    * :mind-blown: x2
    * mix compile

  # Show what the graph looks like (source means go down the tree, sink means go up!)
    * mix xref graph --source lib/a.ex

  # Last example - crazy if folks are interested, Add to A
  # Function defined at compile time, same dependency tree
    * Uncomment if statement, and comment the first 2 lines
    * mix compile
    * mix xref graph --source lib/a.ex
    * iex -S mix
    * > A. <tab, tab>
  """
  @b B.new()
  def new(), do: @b

  # if B.new().id > 3 do
  #   def fxn, do: "big id"
  # else
  #   def fxn, do: "small id"
  # end
end

b.ex

defmodule B do
  @moduledoc "A Compile-time Dependency of A"
  def new, do: C.new()

  def new2, do: C2.new()
end

c.ex

defmodule C do
  @moduledoc "Runtime Dep of B"
  defstruct [:id]
  def new, do: %C{id: 4}
end

c2.ex

defmodule C2 do
  @moduledoc "Runtime Dep of B"
  def new, do: %{id: 3}
end