Mojo C++ bindings: custom type mapping of map

mojo/public/cpp/bindings/lib/serialization_util.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_SERIALIZATION_UTIL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 209 matching lines @@
   return f(std::forward<InputUserType>(input), context);
 }
 
 template <typename ReturnType, typename ParamType, typename InputUserType>
 ReturnType CallWithContext(ReturnType (*f)(ParamType),
                            InputUserType&& input,
                            void* context) {
   return f(std::forward<InputUserType>(input));
 }
 
+template <typename T, typename MaybeConstUserType>
+struct HasGetDataMethod {
+  template <typename U>
+  static char Test(decltype(U::GetData(std::declval<MaybeConstUserType&>()))*);
+  template <typename U>
+  static int Test(...);
+  static const bool value = sizeof(Test<T>(0)) == sizeof(char);
+
+ private:
+  EnsureTypeIsComplete<T> check_t_;
+};
+
+template <
+    typename Traits,
+    typename MaybeConstUserType,
+    typename std::enable_if<
+        HasGetDataMethod<Traits, MaybeConstUserType>::value>::type* = nullptr>
+decltype(Traits::GetData(std::declval<MaybeConstUserType&>()))
+CallGetDataIfExists(MaybeConstUserType& input) {
+  return Traits::GetData(input);
+}
+
+template <
+    typename Traits,
+    typename MaybeConstUserType,
+    typename std::enable_if<
+        !HasGetDataMethod<Traits, MaybeConstUserType>::value>::type* = nullptr>
+void* CallGetDataIfExists(MaybeConstUserType& input) {
+  return nullptr;
+}
+
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SERIALIZATION_UTIL_H_