update to_iso8601 to work on iodata

Author: dkuku

lib/elixir/lib/calendar/datetime.ex

@@ -1107,8 +1107,11 @@ defmodule DateTime do
       std_offset: std_offset
     } = datetime
 
-    datetime_to_string(year, month, day, hour, minute, second, microsecond, format) <>
-      Calendar.ISO.offset_to_string(utc_offset, std_offset, time_zone, format)
+    [
+      datetime_to_iodata(year, month, day, hour, minute, second, microsecond, format),
+      Calendar.ISO.offset_to_iodata(utc_offset, std_offset, time_zone, format)
+    ]
+    |> IO.iodata_to_binary()
   end
 
   def to_iso8601(
@@ -1119,17 +1122,41 @@ defmodule DateTime do
       when format in [:extended, :basic] do
     {year, month, day, hour, minute, second, {microsecond, _}} = shift_by_offset(datetime, 0)
 
-    datetime_to_string(year, month, day, hour, minute, second, {microsecond, precision}, format) <>
-      "Z"
+    [
+      datetime_to_iodata(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second,
+        {microsecond, precision},
+        format
+      ),
+      ?Z
+    ]
+    |> IO.iodata_to_binary()
   end
 
   def to_iso8601(%{calendar: Calendar.ISO} = datetime, format, offset)
       when format in [:extended, :basic] do
     {_, precision} = datetime.microsecond
     {year, month, day, hour, minute, second, {microsecond, _}} = shift_by_offset(datetime, offset)
 
-    datetime_to_string(year, month, day, hour, minute, second, {microsecond, precision}, format) <>
-      Calendar.ISO.offset_to_string(offset, 0, nil, format)
+    [
+      datetime_to_iodata(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second,
+        {microsecond, precision},
+        format
+      ),
+      Calendar.ISO.offset_to_iodata(offset, 0, nil, format)
+    ]
+    |> IO.iodata_to_binary()
   end
 
   def to_iso8601(%{calendar: _} = datetime, format, offset) when format in [:extended, :basic] do
@@ -1148,10 +1175,12 @@ defmodule DateTime do
     |> calendar.naive_datetime_from_iso_days()
   end
 
-  defp datetime_to_string(year, month, day, hour, minute, second, microsecond, format) do
-    Calendar.ISO.date_to_string(year, month, day, format) <>
-      "T" <>
-      Calendar.ISO.time_to_string(hour, minute, second, microsecond, format)
+  defp datetime_to_iodata(year, month, day, hour, minute, second, microsecond, format) do
+    [
+      Calendar.ISO.date_to_iodata(year, month, day, format),
+      "T",
+      Calendar.ISO.time_to_iodata(hour, minute, second, microsecond, format)
+    ]
   end
 
   @doc """

lib/elixir/lib/calendar/naive_datetime.ex

@@ -940,8 +940,12 @@ defmodule NaiveDateTime do
       microsecond: microsecond
     } = naive_datetime
 
-    Calendar.ISO.date_to_string(year, month, day, format) <>
-      "T" <> Calendar.ISO.time_to_string(hour, minute, second, microsecond, format)
+    [
+      Calendar.ISO.date_to_iodata(year, month, day, format),
+      ?T,
+      Calendar.ISO.time_to_iodata(hour, minute, second, microsecond, format)
+    ]
+    |> IO.iodata_to_binary()
   end
 
   def to_iso8601(%{calendar: _} = naive_datetime, format) when format in [:basic, :extended] do