Fix skema default value when create new struct

lib/schema.ex

@@ -247,13 +247,24 @@ defmodule Skema.Schema do
 
       unquote(block)
 
+      definitions = Enum.map(@ts_fields, fn {name, opts} ->
+        {name, Skema.Schema.__default_value__(opts[:default])}
+      end)
+
       @enforce_keys @ts_enforce_keys
-      defstruct @ts_fields
+      defstruct definitions
 
       Skema.Schema.__type__(@ts_types)
     end
   end
 
+  # expand default value, this only applied a single time at build time
+  def __default_value__(default) when is_function(default, 0) do
+    default.()
+  end
+
+  def __default_value__(default), do: default
+
   @doc false
   defmacro __type__(types) do
     quote bind_quoted: [types: types] do

mix.exs

@@ -4,7 +4,7 @@ defmodule Skema.MixProject do
   def project do
     [
       app: :skema,
-      version: "0.2.0",
+      version: "0.2.1",
       elixir: "~> 1.10",
       start_permanent: Mix.env() == :prod,
       deps: deps(),

test/defschema_test.exs

@@ -2,6 +2,23 @@ defmodule DefSchemaTest do
   use ExUnit.Case
   use Skema
 
+
+  describe "defschema module with default value" do
+    defschema User do
+      field(:name, :string, required: true)
+      field(:email, :string, length: [min: 5])
+      field(:age, :integer, default: 10)
+    end
+
+    test "new with default value" do
+      assert  %User{age: 10, name: nil, email: nil} = User.new(%{})
+    end
+
+    test "new override default value" do
+      assert  %User{age: 18, name: "Donkey", email: nil} = User.new(%{age: 18, name: "Donkey"})
+    end
+  end
+
   describe "Skema.cast_and_validate" do
     defschema UserModel do
       field(:name, :string, required: true)