Add data.Marshaler

data/convert.go

@@ -28,6 +28,11 @@ func NewWith(convert StructOptions, value interface{}) Value {
 		return Null{}
 	}
 
+	// see if value implements MarshalValue
+	if mar, ok := value.(Marshaler); ok {
+		return mar.MarshalValue()
+	}
+
 	// drill through pointers and interfaces to the underlying type
 	var v = reflect.ValueOf(value)
 	for v.Kind() == reflect.Interface || v.Kind() == reflect.Ptr {
@@ -103,3 +108,9 @@ func (c StructOptions) Data(obj interface{}) Map {
 	}
 	return Map(m)
 }
+
+// Marshaler is the interface implemented by entities that can marshal
+// themselves into a data.Value.
+type Marshaler interface {
+	MarshalValue() Value
+}

data/convert_test.go

@@ -50,6 +50,10 @@ func TestNew(t *testing.T) {
 			PI *AInt
 		}{{nil}},
 			List{Map{"pI": Null{}}}},
+		{testIDURL{1, "https://github.com/robfig/soy"},
+			Map{"iD": Int(1), "uRL": String("https://github.com/robfig/soy")}},
+		{testIDURLMarshaler{1, "https://github.com/robfig/soy"},
+			Map{"id": Int(1), "url": String("https://github.com/robfig/soy")}},
 	}
 
 	for _, test := range tests {
@@ -60,6 +64,20 @@ func TestNew(t *testing.T) {
 	}
 }
 
+type testIDURL struct {
+	ID  int
+	URL string
+}
+
+type testIDURLMarshaler testIDURL
+
+func (t testIDURLMarshaler) MarshalValue() Value {
+	return Map{
+		"id":  New(t.ID),
+		"url": New(t.URL),
+	}
+}
+
 func TestStructOptions(t *testing.T) {
 	var testStruct = struct {
 		CaseFormat int