If and unless behave differently - compilation error

Phoenix Forum Questions / Help
,
1

My code which compiles:

defmodule MyModule do
  use Plug.Builder


  if System.get_env("MIX_ENV") == "prod" do
    # [......]
  end
end

but

defmodule MyModule do
  use Plug.Builder


  unless System.get_env("MIX_ENV") == "prod" do
    # [......]
  end
end

won’t:

== Compilation error in file lib/web/my_module.ex ==
** (FunctionClauseError) no function clause matching in String.split/3    
    
    The following arguments were given to String.split/3:
    
        # 1
        nil
    
        # 2
        "/"
    
        # 3
        []
    
    Attempted function clauses (showing 3 out of 3):
    
        def split(string, %Regex{} = pattern, options) when is_binary(string)
        def split(string, "", options) when is_binary(string)
        def split(string, pattern, options) when is_binary(string)
    
    (elixir 1.10.4) lib/string.ex:471: String.split/3
    lib/plug/router/utils.ex:120: Plug.Router.Utils.split/1
    lib/plug/static.ex:158: Plug.Static.init/1
    lib/plug/builder.ex:304: Plug.Builder.init_module_plug/4
    lib/plug/builder.ex:288: anonymous fn/5 in Plug.Builder.compile/3
    (elixir 1.10.4) lib/enum.ex:2111: Enum."-reduce/3-lists^foldl/2-0-"/3
    lib/plug/builder.ex:286: Plug.Builder.compile/3
    expanding macro: Plug.Builder.__before_compile__/1

And vise versa:

  # compilation error
  if System.get_env("MIX_ENV") != "prod" do
    # [......]
  end

  # compiles
  unless System.get_env("MIX_ENV") != "prod" do
    # [......]
  end

Why?

Also, what’s a reliable way, nowadays, to determine the current enviroment from within a Phoenix project itself and an Elixir library that’ll be used in a Phoenix project? I deploy my projects via mix, manually.

update1

It can be due to the fact that inside that condition if or unless I have this:

 @cfg Application.get_env(:my_lib, MyLib)
 plug(Plug.Static,
   at: @cfg[:path1],
   from: @cfg[:path2]
 )

and I comment this out, both if or unless will compile.

But why is this an issue? Previously, I used it with no compilation error.

2

Neither if nor unless use String.split, perhaps it’s in your body. Can you share more details?

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