Inline List.flatten/1 and List.flatten/2

Author: devinus

lib/elixir/lib/list.ex

@@ -194,6 +194,8 @@ defmodule List do
 
   Empty list elements are discarded.
 
+  Inlined by the compiler.
+
   ## Examples
 
       iex> List.flatten([1, [[2], 3]])
@@ -204,9 +206,7 @@ defmodule List do
 
   """
   @spec flatten(deep_list) :: list when deep_list: [any | deep_list]
-  def flatten(list) do
-    :lists.flatten(list)
-  end
+  defdelegate flatten(list), to: :lists
 
   @doc """
   Flattens the given `list` of nested lists.
@@ -216,6 +216,8 @@ defmodule List do
   Empty list elements from `list` are discarded,
   but not the ones from `tail`.
 
+  Inlined by the compiler.
+
   ## Examples
 
       iex> List.flatten([1, [[2], 3]], [4, 5])
@@ -226,9 +228,7 @@ defmodule List do
 
   """
   @spec flatten(deep_list, [elem]) :: [elem] when elem: var, deep_list: [elem | deep_list]
-  def flatten(list, tail) do
-    :lists.flatten(list, tail)
-  end
+  defdelegate flatten(list, tail), to: :lists
 
   @doc """
   Folds (reduces) the given list from the left with

lib/elixir/src/elixir_rewrite.erl

@@ -139,6 +139,8 @@ inline(Mod, Fun, Arity) -> inner_inline(ex_to_erl, Mod, Fun, Arity).
 ?inline(?kernel, trunc, 1, erlang, trunc);
 ?inline(?kernel, tuple_size, 1, erlang, tuple_size);
 
+?inline(?list, flatten, 1, lists, flatten);
+?inline(?list, flatten, 2, lists, flatten);
 ?inline(?list, to_atom, 1, erlang, list_to_atom);
 ?inline(?list, to_existing_atom, 1, erlang, list_to_existing_atom);
 ?inline(?list, to_float, 1, erlang, list_to_float);

lib/elixir/test/elixir/code_test.exs

@@ -467,7 +467,7 @@ defmodule CodeTest do
 
     test "disables tail call optimization at the root" do
       try do
-        Code.compile_string("List.flatten(123)")
+        Code.compile_string("List.last(123)")
       rescue
         _ -> assert Enum.any?(__STACKTRACE__, &match?({_, :__FILE__, 1, _}, &1))
       end

lib/elixir/test/elixir/kernel/expansion_test.exs

@@ -1134,8 +1134,8 @@ defmodule Kernel.ExpansionTest do
     end
 
     test "expands remotes" do
-      assert expand(quote(do: &List.flatten/2)) ==
-               quote(do: &:"Elixir.List".flatten/2)
+      assert expand(quote(do: &List.first/2)) ==
+               quote(do: &:"Elixir.List".first/2)
                |> clean_meta([:imports, :context])
 
       assert expand(quote(do: &Kernel.is_atom/1)) ==

lib/elixir/test/elixir/kernel/fn_test.exs

@@ -90,9 +90,9 @@ defmodule Kernel.FnTest do
 
   test "capture with variable module" do
     mod = List
-    assert (&mod.flatten(&1)).([1, [2], 3]) == [1, 2, 3]
-    assert (&mod.flatten/1).([1, [2], 3]) == [1, 2, 3]
-    assert (&mod.flatten/1) == (&List.flatten/1)
+    assert (&mod.first(&1)).([1, 2, 3]) == 1
+    assert (&mod.first/1).([1, 2, 3]) == 1
+    assert (&mod.first/1) == (&List.first/1)
   end
 
   test "local partial application" do

lib/elixir/test/erlang/function_test.erl

@@ -120,8 +120,8 @@ function_call_with_parens_args_and_nested_when_test() ->
 %% Partial application
 
 require_partial_application_test() ->
-  {Fun, _} = eval("&List.flatten(&1)"),
-  Fun = fun 'Elixir.List':flatten/1.
+  {Fun, _} = eval("&List.first(&1)"),
+  Fun = fun 'Elixir.List':first/1.
 
 import_partial_application_test() ->
   {Fun, _} = eval("&is_atom(&1)"),