Elixir - Define functions in module by metaprogramming

Question

I have three identical methods in my module, that do (almost) exactly the same thing. Instead of repeating the function definitions, I am trying to define them once to keep code minimal and same for all of them.

So far I've tried using Code.eval_string:

defmodule MyModule do
  Enum.each ~w(method1 method2 method3), fn method ->
    @method method

    Code.eval_string """
      def #{@method}(map) when is_map(map) do
        do_map_stuff(:#{@method}, map)
      end

      def #{@method}(arg) do
        do_other_stuff(:#{@method}, arg)
      end
    """
  end

  ## Other Methods

end

but this throws ArgumentError:

Compiling 1 file (.ex)
** (ArgumentError) cannot invoke def/2 outside module
    (elixir) lib/kernel.ex:4297: Kernel.assert_module_scope/3
    (elixir) lib/kernel.ex:3299: Kernel.define/4
    (elixir) expanding macro: Kernel.def/2
    nofile:1: (file)

I think quote/unquote might be the way to go, but I'm not exactly sure how to do this using them (I've already read the Meta Guide on the Elixir website).

Sheharyar · Accepted Answer · 2019-03-26 19:37:53Z

4

Something like this?

defmodule MyModule do
  def do_map_stuff(method, arg) do
    IO.inspect([method, arg])
  end

  Enum.each [:method1, :method2, :method3], fn method ->
    def unquote(method)(map) when is_map(map) do
      do_map_stuff(unquote(method), map)
    end

    def unquote(method)(arg)  do
      do_map_stuff(unquote(method), arg)
    end
  end
end

edited Mar 26, 2019 at 19:37

Sheharyar

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answered Oct 25, 2016 at 22:01

rorra

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1 Comment

Sheharyar Over a year ago

I updated it to use atoms instead of strings which suit my case better (and also look much more cleaner and readable!)

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