Allow records without field default values

Author: ericmj

lib/elixir/lib/kernel.ex

@@ -3299,15 +3299,11 @@ defmodule Kernel do
   In case a struct does not declare a field type, it defaults to `term`.
   """
   defmacro defstruct(kv) do
-    {fields, types} = Record.Backend.split_fields_and_types(:defstruct, kv)
+    {fields, types} = Record.Backend.split_fields_and_types(kv)
 
     fields =
       quote bind_quoted: [fields: fields] do
-        fields = Enum.map(fields, fn
-          { key, _ } = pair when is_atom(key) -> pair
-          key when is_atom(key) -> { key, nil }
-          other -> raise ArgumentError, message: "struct fields must be atoms, got: #{inspect other}"
-        end)
+        fields = Record.Backend.default_fields(:struct, fields)
 
         def __struct__() do
           %{unquote_splicing(Macro.escape(fields)), __struct__: __MODULE__}

lib/elixir/lib/record.ex

@@ -157,7 +157,7 @@ defmodule Record do
   defmacro defrecord(name, tag \\ nil, kv) do
     quote bind_quoted: [name: name, tag: tag, kv: kv] do
       tag = tag || name
-      fields = Macro.escape(kv)
+      fields = Macro.escape Record.Backend.default_fields(:record, kv)
 
       defmacro(unquote(name)(args \\ [])) do
         Record.Backend.access(unquote(tag), unquote(fields), args, __CALLER__)
@@ -175,7 +175,7 @@ defmodule Record do
   defmacro defrecordp(name, tag \\ nil, kv) do
     quote bind_quoted: [name: name, tag: tag, kv: kv] do
       tag = tag || name
-      fields = Macro.escape(kv)
+      fields = Macro.escape Record.Backend.default_fields(:record, kv)
 
       defmacrop(unquote(name)(args \\ [])) do
         Record.Backend.access(unquote(tag), unquote(fields), args, __CALLER__)

lib/elixir/lib/record/backend.ex

@@ -2,32 +2,43 @@ defmodule Record.Backend do
   # Callback functions invoked by defrecord, defrecordp and friends.
   @moduledoc false
 
+  @doc """
+  Normalizes a list of record or struct fields to have default values.
+  """
+  def default_fields(type, fields) do
+    Enum.map(fields, fn
+      { key, _ } = pair when is_atom(key) -> pair
+      key when is_atom(key) -> { key, nil }
+      other -> raise ArgumentError, message: "#{type} fields must be atoms, got: #{inspect other}"
+    end)
+  end
+
   @doc """
   Splits a keywords list into fields and types.
 
   This logic is shared by records and structs.
   """
-  def split_fields_and_types(tag, kv) do
+  def split_fields_and_types(kv) do
     if Keyword.keyword?(kv) do
-      split_fields_and_types(tag, kv, [], [])
+      split_fields_and_types(kv, [], [])
     else
       {kv, []}
     end
   end
 
-  defp split_fields_and_types(tag, [{field, {:::, _, [default, type]}}|t], fields, types) do
-    split_fields_and_types(tag, t, [{field, default}|fields], [{field, type}|types])
+  defp split_fields_and_types([{field, {:::, _, [default, type]}}|t], fields, types) do
+    split_fields_and_types(t, [{field, default}|fields], [{field, type}|types])
   end
 
-  defp split_fields_and_types(tag, [{field, default}|t], fields, types) do
-    split_fields_and_types(tag, t, [{field, default}|fields], [{field, quote(do: term)}|types])
+  defp split_fields_and_types([{field, default}|t], fields, types) do
+    split_fields_and_types(t, [{field, default}|fields], [{field, quote(do: term)}|types])
   end
 
-  defp split_fields_and_types(tag, [field|t], fields, types) do
-    split_fields_and_types(tag, t, [{field, nil}|fields], [{field, quote(do: term)}|types])
+  defp split_fields_and_types([field|t], fields, types) do
+    split_fields_and_types(t, [field|fields], [{field, quote(do: term)}|types])
   end
 
-  defp split_fields_and_types(_tag, [], fields, types) do
+  defp split_fields_and_types([], fields, types) do
     {:lists.reverse(fields), :lists.reverse(types)}
   end
 

lib/elixir/test/elixir/record_test.exs

@@ -50,6 +50,7 @@ defmodule RecordTest do
     refute record?(13)
   end
 
+  Record.defrecord  :timestamp, [:date, :time]
   Record.defrecord  :user, __MODULE__, name: "José", age: 25
   Record.defrecordp :file_info, Record.extract(:file_info, from_lib: "kernel/include/file.hrl")
 
@@ -81,4 +82,14 @@ defmodule RecordTest do
     assert macro_exported?(__MODULE__, :user, 0)
     refute macro_exported?(__MODULE__, :file_info, 1)
   end
+
+  test "records with no defaults" do
+    record = timestamp()
+    assert timestamp(record, :date) == nil
+    assert timestamp(record, :time) == nil
+
+    record = timestamp(date: :foo, time: :bar)
+    assert timestamp(record, :date) == :foo
+    assert timestamp(record, :time) == :bar
+  end
 end