Implement unions as members of structs.

mojo/public/cpp/bindings/lib/array_internal.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_INTERNAL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_INTERNAL_H_
 
 #include <new>
 #include <vector>
 
@@ skipping 267 matching lines @@
       }
       if (!ValidateCaller<P, ElementValidateParams>::Run(
               DecodePointerRaw(&elements[i].offset), bounds_checker)) {
         return false;
       }
     }
     return true;
   }
 
  private:
+  template <typename T,
+            typename Params,
+            bool is_union = IsUnionDataType<T>::value>
+  struct ValidateCaller {};
+
   template <typename T, typename Params>
-  struct ValidateCaller {
+  struct ValidateCaller<T, Params, false> {
     static bool Run(const void* data, BoundsChecker* bounds_checker) {
       static_assert((IsSame<Params, NoValidateParams>::value),
                     "Struct type should not have array validate params");
 
       return T::Validate(data, bounds_checker);
     }
   };
 
+  template <typename T, typename Params>
+  struct ValidateCaller<T, Params, true> {
+    static bool Run(const void* data, BoundsChecker* bounds_checker) {
+      static_assert((IsSame<Params, NoValidateParams>::value),
+                    "Union type should not have array validate params");
+
+      return T::Validate(data, bounds_checker, true);
+    }
+  };
+
   template <typename Key, typename Value, typename Params>
-  struct ValidateCaller<Map_Data<Key, Value>, Params> {
+  struct ValidateCaller<Map_Data<Key, Value>, Params, false> {
     static bool Run(const void* data, BoundsChecker* bounds_checker) {
       return Map_Data<Key, Value>::template Validate<Params>(data,
                                                              bounds_checker);
     }
   };
 
   template <typename T, typename Params>
-  struct ValidateCaller<Array_Data<T>, Params> {
+  struct ValidateCaller<Array_Data<T>, Params, false> {
     static bool Run(const void* data, BoundsChecker* bounds_checker) {
       return Array_Data<T>::template Validate<Params>(data, bounds_checker);
     }
   };
 };
 
 template <typename T>
 class Array_Data {
  public:
   typedef ArrayDataTraits<T> Traits;
@@ skipping 185 matching lines @@
 
 template <>
 struct WrapperTraits<String, false> {
   typedef String_Data* DataType;
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_ARRAY_INTERNAL_H_