allows for encoding keyword lists (#62)

added a method to do encodings directly through keyword lists

lib/encode.ex

@@ -150,19 +150,30 @@ defmodule Jason.Encode do
      | list_loop(tail, escape, encode_map)]
   end
 
+  @spec keyword(keyword, opts) :: iodata
+  def keyword(list, {escape, encode_map}) do
+    encode_map.(list, escape, encode_map)
+  end
+
   @spec map(map, opts) :: iodata
   def map(value, {escape, encode_map}) do
     encode_map.(value, escape, encode_map)
   end
 
+  defp map_naive([], _escape, _encode_map) do
+    "{}"
+  end
+
+  defp map_naive([{key, value} | tail], escape, encode_map) do
+    ["{\"", key(key, escape), "\":",
+    value(value, escape, encode_map)
+    | map_naive_loop(tail, escape, encode_map)]
+  end
+
   defp map_naive(value, escape, encode_map) do
-    case Map.to_list(value) do
-      [] -> "{}"
-      [{key, value} | tail] ->
-        ["{\"", key(key, escape), "\":",
-         value(value, escape, encode_map)
-         | map_naive_loop(tail, escape, encode_map)]
-    end
+    value
+    |> Map.to_list
+    |> map_naive(escape, encode_map)
   end
 
   defp map_naive_loop([], _escape, _encode_map) do
@@ -175,16 +186,22 @@ defmodule Jason.Encode do
      | map_naive_loop(tail, escape, encode_map)]
   end
 
+  defp map_strict([], _escape, _encode_map) do
+    "{}"
+  end
+
+  defp map_strict([{key, value} | tail], escape, encode_map) do
+    key = IO.iodata_to_binary(key(key, escape))
+    visited = %{key => []}
+    ["{\"", key, "\":",
+     value(value, escape, encode_map)
+     | map_strict_loop(tail, escape, encode_map, visited)]
+  end
+
   defp map_strict(value, escape, encode_map) do
-    case Map.to_list(value) do
-      [] -> "{}"
-      [{key, value} | tail] ->
-        key = IO.iodata_to_binary(key(key, escape))
-        visited = %{key => []}
-        ["{\"", key, "\":",
-         value(value, escape, encode_map)
-         | map_strict_loop(tail, escape, encode_map, visited)]
-    end
+    value
+    |> Map.to_list
+    |> map_strict(escape, encode_map)
   end
 
   defp map_strict_loop([], _encode_map, _escape, _visited) do

test/encode_test.exs

@@ -133,6 +133,24 @@ defmodule Jason.EncoderTest do
     assert to_json(derived_using_except) == ~s({"size":10})
   end
 
+  defmodule KeywordTester do
+    defstruct [:baz, :foo, :quux]
+  end
+
+  defimpl Jason.Encoder, for: [KeywordTester] do
+    def encode(struct, opts) do
+      struct
+      |> Map.from_struct
+      |> Enum.map(&(&1))
+      |> Jason.Encode.keyword(opts)
+    end
+  end
+
+  test "using keyword list encoding" do
+    t = %KeywordTester{baz: :bar, foo: "bag", quux: 42}
+    assert to_json(t) == ~s({"baz":"bar","foo":"bag","quux":42})
+  end
+
   test "EncodeError" do
     assert_raise Protocol.UndefinedError, fn ->
       to_json(self())
@@ -162,4 +180,5 @@ defmodule Jason.EncoderTest do
   defp to_json(value, opts \\ []) do
     Jason.encode!(value, opts)
   end
+
 end