Mojo C++ bindings: custom type mapping of map

mojo/public/cpp/bindings/map_traits_stl.h

+// Copyright 2016 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_MAP_TRAITS_STL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_STL_H_
+
+#include <map>
+
+#include "mojo/public/cpp/bindings/map_traits.h"
+
+namespace mojo {
+
+template <typename K, typename V>
+struct MapTraits<std::map<K, V>> {
+  using Key = K;
+  using Value = V;
+  using Iterator = typename std::map<K, V>::iterator;
+  using ConstIterator = typename std::map<K, V>::const_iterator;
+
+  static bool IsNull(const std::map<K, V>& input) {
+    // std::map<> is always converted to non-null mojom map.
+    return false;
+  }
+
+  static void SetToNull(std::map<K, V>* output) {
+    // std::map<> doesn't support null state. Set it to empty instead.
+    output->clear();
+  }
+
+  static size_t GetSize(const std::map<K, V>& input) { return input.size(); }
+
+  static ConstIterator GetBegin(const std::map<K, V>& input) {
+    return input.begin();
+  }
+  static Iterator GetBegin(std::map<K, V>& input) { return input.begin(); }
+
+  static void AdvanceIterator(ConstIterator& iterator) { iterator++; }
+  static void AdvanceIterator(Iterator& iterator) { iterator++; }
+
+  static const K& GetKey(Iterator& iterator) { return iterator->first; }
+  static const K& GetKey(ConstIterator& iterator) { return iterator->first; }
+
+  static V& GetValue(Iterator& iterator) { return iterator->second; }
+  static const V& GetValue(ConstIterator& iterator) { return iterator->second; }
+
+  static void Insert(std::map<K, V>& input, const K& key, V&& value) {
+    input.insert(std::make_pair(key, std::forward<V>(value)));
+  }
+  static void Insert(std::map<K, V>& input, const K& key, const V& value) {
+    input.insert(std::make_pair(key, value));
+  }
+
+  static void SetToEmpty(std::map<K, V>* output) { output->clear(); }
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_MAP_TRAITS_STL_H_