Convert Module name to String and back to module

Question

If we have a module name like this:

 Module.V1.CountryTest

I can convert it to String like this:

   Module.V1.CountryTest |> to_string

Now there are some interesting results I am getting on iex

   module = Module.V1.CountryTest |> to_string
         "Elixir.Module.V1.CountryTest"
   iex(2)> replace = Regex.replace(~r/Test/, module, "")
        "Elixir.Module.V1.Country"
   iex(3)> replace |> String.to_atom
         Module.V1.Country

So if I remove Test. And convert it back to atom. It will give me back the module name. But If I replace or remove anything else from the module name it gives me this output:

   some = Regex.replace(~r/Country/, replace, "")
     "Elixir.Module.V1."
   iex(5)> some |> String.to_atom
     :"Elixir.Module.V1."

Can anybody please explain this behavior? And why it wont allow any other parts to change or replace. Meaning giving me back the output like this

 Module.V1.Country

I mean if its possible.

Thanks.

Answer 1

Elixir module names are just atoms prefixed with "Elixir.". Elixir prints atoms which start with "Elixir." and contain a valid Elixir module name after that differently than other atoms:

iex(1)> :"Elixir.Foo"
Foo
iex(2)> :"Elixir.F-o"
:"Elixir.F-o"

When you replace Test, the rest of the value is a valid Elixir module name, but when you replace Country as well, you end up with a . at the end which is not a valid module name. If you remove the dot too, you'll get what you want:

iex(3)> Module.V1.Country |> to_string |> String.replace(~r/Country/, "") |> String.to_atom
:"Elixir.Module.V1."
iex(4)> Module.V1.Country |> to_string |> String.replace(~r/\.Country/, "") |> String.to_atom
Module.V1

Answer 2

To convert a string to a module, you may want to use Module.safe_concat/1 or /2:

Module.safe_concat(Module.V1, "CountryTest") # => Module.V1.CountryTest
Module.safe_concat(~w[Module V1 CountryTest]) # => Module.V1.CountryTest