Handle dashed keys, like in jsonapi.org recommendations.

lib/poison/decoder.ex

@@ -48,7 +48,12 @@ defmodule Poison.Decode do
   defp transform_struct(value, keys, as, options) do
     Map.from_struct(as)
     |> Enum.reduce(%{}, fn {key, default}, acc ->
-      Map.put(acc, key, Map.get(value, Atom.to_string(key), default))
+      string_key = if options[:dash] do
+        key |> Atom.to_string() |> String.replace("_", "-")
+      else
+        key |> Atom.to_string()
+      end
+      Map.put(acc, key, Map.get(value, string_key, default))
     end)
     |> do_transform_struct(keys, as, options)
   end

lib/poison/encoder.ex

@@ -81,9 +81,14 @@ defimpl Poison.Encoder, for: BitString do
   def encode("", _), do: "\"\""
 
   def encode(string, options) do
-    [?", escape(string, options[:escape]), ?"]
+    [?", dash(string, options[:dash]) |> escape(options[:escape]), ?"]
   end
 
+  defp dash(string, true) when is_binary(string) do
+    String.replace(string, "_", "-")
+  end
+  defp dash(string, _), do: string
+
   defp escape("", _), do: []
 
   for {char, seq} <- Enum.zip('"\\\n\t\r\f\b', '"\\ntrfb') do

test/poison/decoder_test.exs

@@ -23,6 +23,10 @@ defmodule Poison.DecoderTest do
     defstruct [:email, :telephone, call_count: 0]
   end
 
+  defmodule PersonDash do
+    defstruct [:person_name, :address, :contact, age: 42]
+  end
+
   defimpl Poison.Decoder, for: Address do
     def decode(address, _options) do
       "#{address.street}, #{address.city}, #{address.state}  #{address.zip}"
@@ -34,6 +38,11 @@ defmodule Poison.DecoderTest do
     assert decode(person, as: %Person{}) == %Person{name: "Devin Torres", age: 27}
   end
 
+  test "decoding single :as with string-dash keys" do
+    person = %{"person-name" => "Devin Torres", "age" => 27}
+    assert decode(person, as: %PersonDash{}, dash: true) == %PersonDash{person_name: "Devin Torres", age: 27}
+  end
+
   test "decoding single :as with atom keys" do
     person = %{name: "Devin Torres", age: 27}
     assert decode(person, keys: :atoms!, as: %Person{}) == %Person{name: "Devin Torres", age: 27}

test/poison/encoder_test.exs

@@ -32,6 +32,7 @@ defmodule Poison.EncoderTest do
     assert to_json("\u2028\u2029", escape: :javascript) == ~s("\\u2028\\u2029")
     assert to_json("</script>", escape: :html_safe) == ~s("<\\/script>")
     assert to_json("áéíóúàèìòùâêîôûãẽĩõũ") == ~s("áéíóúàèìòùâêîôûãẽĩõũ")
+    assert to_json("hello_world", dash: true) == ~s("hello-world")
   end
 
   test "Map" do