__using__ macro with option

[mruoss]

@Eiji

I have used atom as it’s best for what I called feature_name as those in apply_feature/1 are known at compile-time. You can use strings, integers and every other data that you can write pattern-matching for.

Not maps. Or structs. You can’t expand those to their original value either. You’d have to call Code.eval_quoted() which is discouraged inside macros, no?

I’d like come back to my original question. I have changed the example to take a map. It does not make much sense like this and could be done better, but it is a simple example to show the case with a map as option value:

defmodule UsedModule do
  defmacro __using__(opts) do
    quote do
      if unquote(opts[:with_extra]) do
        def extra(), do: "with extra"
      else
        def extra(), do: "no extra"
      end
    end
  end
end

defmodule UsingModuleWithExtra, do: use UsedModule, config: %{with_extra: true}
defmodule UsingModuleNoExtra, do: use UsedModule

iex> UsingModuleWithExtra.extra()
"with extra"

iex> UsingModuleNoExtra.extra()
"no extra"

See the passed option is expected to be a map. Which cannot be expanded to its original value. You have to unquote them inside a quote block (right?). So my question was, if you would - in this case where the argument requires unquoting - implement the macro like I did above or rather put the if condition inside the generated function like this:

def extra() do
  if Keyword.get(opts, :config, %{})[:with_extra], 
    do: "with extra", 
    else: "no extra"
end