mojom: Add associative arrays to the mojom language.

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

+// Copyright 2014 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_MAP_INTERNAL_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_MAP_INTERNAL_H_
+
+#include <map>
+
+#include "mojo/public/cpp/bindings/array.h"
+#include "mojo/public/cpp/bindings/lib/bindings_internal.h"
+
+namespace mojo {
+namespace internal {
+
+template <typename Key, typename Value, bool kValueIsMoveOnlyType>
+struct MapTraits {};
+
+template <typename Key, typename Value>
+struct MapTraits<Key, Value, false> {
+  // Map keys can't be move only types.
+  static_assert(!internal::IsMoveOnlyType<Key>::value,
+                "Map keys can not be move only types.");
+
+  typedef Key KeyStorageType;
+  typedef Key& KeyRefType;
+  typedef const Key& KeyConstRefType;
+  typedef KeyConstRefType KeyForwardType;
+
+  typedef Value ValueStorageType;
+  typedef Value& ValueRefType;
+  typedef const Value& ValueConstRefType;
+  typedef ValueConstRefType ValueForwardType;
+
+  static inline void InitializeFrom(
+      std::map<KeyStorageType, ValueStorageType>* m,
+      mojo::Array<Key> keys,
+      mojo::Array<Value> values) {
+    for (size_t i = 0; i < keys.size(); ++i)
+      Insert(m, keys[i], values[i]);
+  }
+  static inline void Decompose(std::map<KeyStorageType, ValueStorageType>* m,
+                               mojo::Array<Key>* keys,
+                               mojo::Array<Value>* values) {
+    keys->resize(m->size());
+    values->resize(m->size());
+    int i = 0;
+    for (typename std::map<KeyStorageType, ValueStorageType>::iterator
+             it = m->begin();
+         it != m->end();
+         ++it, ++i) {
+      (*keys)[i] = it->first;
+      (*values)[i] = it->second;
+    }
+  }
+  static inline void Finalize(std::map<KeyStorageType, ValueStorageType>* m) {}
+  static inline ValueRefType at(std::map<KeyStorageType, ValueStorageType>* m,
+                                KeyForwardType key) {
+    // We don't have C++11 library support yet, so we have to emulate the crash
+    // on a non-existant key.
+    auto it = m->find(key);
+    MOJO_CHECK(it != m->end());
+    return it->second;
+  }
+  static inline ValueConstRefType at(
+      const std::map<KeyStorageType, ValueStorageType>* m,
+      KeyForwardType key) {
+    // We don't have C++11 library support yet, so we have to emulate the crash
+    // on a non-existant key.
+    auto it = m->find(key);
+    MOJO_CHECK(it != m->end());
+    return it->second;
+  }
+  static inline void Insert(std::map<KeyStorageType, ValueStorageType>* m,
+                            KeyForwardType key,
+                            ValueForwardType value) {
+    m->insert(std::make_pair(key, value));
+  }
+  static inline KeyConstRefType GetKey(
+      const typename std::map<KeyStorageType, ValueStorageType>::const_iterator&
+          it) {
+    return it->first;
+  }
+  static inline ValueConstRefType GetValue(
+      const typename std::map<KeyStorageType, ValueStorageType>::const_iterator&
+          it) {
+    return it->second;
+  }
+  static inline ValueRefType GetValue(
+      const typename std::map<KeyStorageType, ValueStorageType>::iterator& it) {
+    return it->second;
+  }
+  static inline void Clone(
+      const std::map<KeyStorageType, ValueStorageType>& src,
+      std::map<KeyStorageType, ValueStorageType>* dst) {
+    dst->clear();
+    for (auto it = src.begin(); it != src.end(); ++it)
+      dst->insert(*it);
+  }
+};
+
+template <typename Key, typename Value>
+struct MapTraits<Key, Value, true> {
+  // Map keys can't be move only types.
+  static_assert(!internal::IsMoveOnlyType<Key>::value,
+                "Map keys can not be move only types.");
+
+  typedef Key KeyStorageType;
+  typedef Key& KeyRefType;
+  typedef const Key& KeyConstRefType;
+  typedef KeyConstRefType KeyForwardType;
+
+  struct ValueStorageType {
+    // Make 8-byte aligned.
+    char buf[sizeof(Value) + (8 - (sizeof(Value) % 8)) % 8];
+  };
+  typedef Value& ValueRefType;
+  typedef const Value& ValueConstRefType;
+  typedef Value ValueForwardType;
+
+  static inline void InitializeFrom(
+      std::map<KeyStorageType, ValueStorageType>* m,
+      mojo::Array<Key> keys,
+      mojo::Array<Value> values) {
+    for (size_t i = 0; i < keys.size(); ++i) {
+      // We can't call Insert() directly because of forwarding. Emulate the

[yzshen1, 2014/10/09 17:41:58]

(just out of curiosity) what is the forwarding issue? I haven't understood.

[Elliot Glaysher, 2014/10/09 19:15:19]

Experimented more; calling Insert() directly works if we don't call
Value.Pass(), even through it's a move only type. (Because Insert takes a
ValueRefType instead of a ValueType.)

+      // logic there to ensure that we handle invalid maps with duplicate keys.
+      auto it = m->find(keys[i]);
+      if (it == m->end())
+        new ((*m)[keys[i]].buf) Value(values[i].Pass());
+    }
+  }
+  static inline void Decompose(std::map<KeyStorageType, ValueStorageType>* m,
+                               mojo::Array<Key>* keys,
+                               mojo::Array<Value>* values) {
+    keys->resize(m->size());
+    values->resize(m->size());
+    int i = 0;
+    for (typename std::map<KeyStorageType, ValueStorageType>::iterator
+             it = m->begin();
+         it != m->end();
+         ++it, ++i) {
+      (*keys)[i] = it->first;
+      (*values)[i] = GetValue(it).Pass();
+    }
+  }
+  static inline void Finalize(std::map<KeyStorageType, ValueStorageType>* m) {
+    for (auto& pair : *m)
+      reinterpret_cast<Value*>(pair.second.buf)->~Value();
+  }
+  static inline ValueRefType at(std::map<KeyStorageType, ValueStorageType>* m,
+                                KeyForwardType key) {
+    // We don't have C++11 library support yet, so we have to emulate the crash
+    // on a non-existant key.
+    auto it = m->find(key);
+    MOJO_CHECK(it != m->end());
+    return GetValue(it);
+  }
+  static inline ValueConstRefType at(
+      const std::map<KeyStorageType, ValueStorageType>* m,
+      KeyForwardType key) {
+    // We don't have C++11 library support yet, so we have to emulate the crash
+    // on a non-existant key.
+    auto it = m->find(key);
+    MOJO_CHECK(it != m->end());
+    return GetValue(it);
+  }
+  static inline void Insert(std::map<KeyStorageType, ValueStorageType>* m,
+                            KeyForwardType key,
+                            ValueRefType value) {
+    // STL insert() doesn't insert |value| if |key| is already part of |m|. We
+    // have to use operator[] to initialize into the storage buffer, but we
+    // have to do a manual check so that we don't overwrite an existing object.
+    auto it = m->find(key);
+    if (it == m->end())
+      new ((*m)[key].buf) Value(value.Pass());
+  }
+  static inline KeyConstRefType GetKey(
+      const typename std::map<KeyStorageType, ValueStorageType>::const_iterator&
+          it) {
+    return it->first;
+  }
+  static inline ValueConstRefType GetValue(
+      const typename std::map<KeyStorageType, ValueStorageType>::const_iterator&
+          it) {
+    return *reinterpret_cast<const Value*>(it->second.buf);
+  }
+  static inline ValueRefType GetValue(
+      const typename std::map<KeyStorageType, ValueStorageType>::iterator& it) {
+    return *reinterpret_cast<Value*>(it->second.buf);
+  }
+  static inline void Clone(
+      const std::map<KeyStorageType, ValueStorageType>& src,
+      std::map<KeyStorageType, ValueStorageType>* dst) {
+    Finalize(dst);
+    dst->clear();
+    for (auto it = src.begin(); it != src.end(); ++it)
+      new ((*dst)[it->first].buf) Value(GetValue(it).Clone());
+  }
+};
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_MAP_INTERNAL_H_