defstruct in a dynamically named module?

[Ian Duggan]

Is there some technique for making the code below work?

--Ian

defmodule Module.concat(["Foo"]) do

  defstruct name: nil, age: 5

  def whostruct do

    %__MODULE__{}

  end

end

** (CompileError) tmp/src.exs:5: Foo.__struct__/0 is undefined, cannot expand struct Foo

    (elixir) src/elixir_map.erl:44: :elixir_map.translate_struct/4

    (elixir) src/elixir_clauses.erl:36: :elixir_clauses.clause/7

    (elixir) src/elixir_def.erl:195: :elixir_def.translate_clause/7

    (elixir) src/elixir_def.erl:184: :elixir_def.translate_definition/8

    (elixir) src/elixir_def.erl:95: :elixir_def.store_definition/9

    (elixir) src/elixir.erl:175: :elixir.erl_eval/3

[John W Higgins]

I would suggest two things.

First, I believe the short option would be

def whostruct do

  struct(__MODULE__)

end

But I would strongly suggest you look at creating a macro here to build your module - that's sort of the standard "build it dynamically" concept

Something like this

defmodule ModuleBuilder do
  defmacro build_module(mod_name) do
    quote do
      defmodule unquote(mod_name) do

        defstruct name: nil, age: 5

        def whostruct do

          struct(__MODULE__)
        end
      end
    end
  end
end

defmodule Foo do
  require ModuleBuilder

  ModuleBuilder.build_module(Module.concat([__MODULE__, "Bar"]))
end

Would appear to be a much better choice in my opinion.

The above would end up with a Foo.Bar module that can be called as in Foo.Bar.whostruct

John

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[José Valim]

But I would strongly suggest you look at creating a macro here to build your module - that's sort of the standard "build it dynamically" concept

What would the macro buy us though? The code posted is supposed to work fine. I just need to investigate why it doesn't.

--

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

[José Valim]

Hi Ian, indeed this does looks like a bug. can you please file a report in our issues tracker? Thank you!

José Valim

www.plataformatec.com.br

Skype: jv.ptec

Founder and Director of R&D

--

[Ian Duggan]

Sure thing. FWIW, it seems like it *might* work for compiled files but not from iex. (1.2.5 and 1.3.0). I will investigate a bit when I file the bug today.

--Ian