Elimination of a boilerplate code using macros in Elixir.

catchall.exs

###############################################################################
# Elimination of a boilerplate code using macros in Elixir.
#
# See SO question
#    http://stackoverflow.com/questions/29573944/elixir-generating-catch-all-function-calls
#
# Run with:
#
# $ elixir catchall.exs
# Fun1: handled by user code
# Fun1: handled by catchall
# Fun2: handled by user code
# Fun2: handled by catchall


###############################################################################
# This is a "library code" where boilerplate code helpers are implemented
defmodule FunBase do

  defmacro __using__(_) do
    quote do
      import FunBase, only: [fun1_catchall: 0, fun2_catchall: 0]
    end
  end

  defmacro fun1_catchall do
    quote do
      def fun1(_,_), do: IO.puts("Fun1: handled by catchall")
    end
  end

  defmacro fun2_catchall do
    quote do
      def fun2(_,_), do: IO.puts("Fun2: handled by catchall")
    end
  end

end

###############################################################################
# This is a "user code" with minimum of the boilerplate but still explicit catchall.
defmodule FunImpl do
  use FunBase

  def fun1(1,2), do: IO.puts("Fun1: handled by user code")
  # Instead of a boilerplate code, you use just this one line.
  # Of course it must be after all user fun1(...,...)s
  fun1_catchall

  def fun2(1,2), do: IO.puts("Fun2: handled by user code")
  # instead of a boilerplate code, you use just this one line
  fun2_catchall
end

FunImpl.fun1(1,2)
FunImpl.fun1(3,4)
FunImpl.fun2(1,2)
FunImpl.fun2(3,4)