macro & use in module

0_readme.md

Elixir的macro ＆ use

可以用defmacro __using__來給之用use的modue，module自動產生預設的method

或者新增新的keyword, 雖然非必要不建議新增太多自定的macro elixir的if else或者ExUnit都有用到

1_logger.exs

defmodule Logger do
  defmacro log(msg) do
    if Application.get_env(:logger, :enabled) do
      quote do
        IO.puts("Logged message: #{unquote(msg)}")
      end
    end
  end
end

defmodule Example do
  require Logger

  def test do
    Logger.log("This is a log message")
  end
end

hello.exs

defmodule Hello do
  defmacro __using__(opts) do
    greeting = Keyword.get(opts, :greeting, "Hi")

    quote do
      def hello(name), do: unquote(greeting) <> ", " <> name
    end
  end
end

use_hello.exs

defmodule UseHello do
  use Hello, greeting: "Halo"

  @greeting "Hello"
  def greeting(name) do
    "#{@greeting} #{name}."
  end

end