mojom: Add associative arrays to the mojom language.

mojo/public/cpp/bindings/map.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_MAP_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_MAP_H_
+
+#include <map>
+
+#include "mojo/public/cpp/bindings/lib/map_internal.h"
+
+namespace mojo {
+
+// Provides read-only access to map data.

[yzshen1, 2014/10/03 18:03:38]

What do you mean by it is read-only?

[Elliot Glaysher, 2014/10/03 21:11:49]

This was copied verbatim from array.h, and isn't true there either anymore.

+template <typename Key, typename Value>
+class Map {
+  MOJO_MOVE_ONLY_TYPE_FOR_CPP_03(Map, RValue)
+ public:
+  // Map keys can not be move only classes.
+  MOJO_COMPILE_ASSERT(!internal::IsMoveOnlyType<Key>::value,
+                      map_key_cant_be_move_only);
+
+  typedef internal::MapTraits<Key, Value,
+                              internal::IsMoveOnlyType<Value>::value> Traits;
+  typedef typename Traits::KeyStorageType KeyStorageType;
+  typedef typename Traits::KeyRefType KeyRefType;
+  typedef typename Traits::KeyConstRefType KeyConstRefType;
+  typedef typename Traits::KeyForwardType KeyForwardType;
+
+  typedef typename Traits::ValueStorageType ValueStorageType;
+  typedef typename Traits::ValueRefType ValueRefType;
+  typedef typename Traits::ValueConstRefType ValueConstRefType;
+  typedef typename Traits::ValueForwardType ValueForwardType;
+
+  Map() : is_null_(true) {}
+
+  Map(mojo::Array<Key> keys, mojo::Array<Value> values)
+      : is_null_(false) {
+    MOJO_DCHECK(keys.size() == values.size());
+    Traits::InitializeFrom(&map_, keys.Pass(), values.Pass());
+  }
+
+  ~Map() {
+    Traits::Finalize(&map_);
+  }
+
+  Map(RValue other) : is_null_(true) { Take(other.object); }
+  Map& operator=(RValue other) {
+    Take(other.object);
+    return *this;
+  }
+
+  template <typename U>
+  static Map From(const U& other) {
+    return TypeConverter<Map, U>::Convert(other);
+  }
+
+  template <typename U>
+  U To() const {
+    return TypeConverter<U, Map>::Convert(*this);
+  }
+
+  void reset() {
+    if (!map_.empty()) {
+      Traits::Finalize(&map_);
+      map_.clear();
+    }
+    is_null_ = true;
+  }
+
+  bool is_null() const { return is_null_; }
+
+  size_t size() const { return map_.size(); }
+
+  void insert(KeyForwardType key, ValueForwardType value) {

[yzshen1, 2014/10/03 18:03:38]

Could you please comment about the behavior when |key| already exists in the
map?

+    is_null_ = false;
+    Traits::Insert(&map_, key, value);
+  }
+
+  ValueRefType at(KeyForwardType key) { return Traits::at(&map_, key); }

[yzshen1, 2014/10/03 18:03:38]

I think it is good to have a const version.

+
+  void Swap(Map<Key, Value>* other) {
+    std::swap(is_null_, other->is_null_);
+    map_.swap(other->map_);
+  }
+  void Swap(std::map<Key, Value>* other) {
+    is_null_ = false;
+    map_.swap(*other);
+  }
+
+  // This moves all values in the map to a set of parallel arrays. This action
+  // is destructive because we can have move-only objects as values; therefore
+  // we can't have copy semantics here.
+  void DecomposeMapTo(mojo::Array<Key>* keys, mojo::Array<Value>* values) {
+    Traits::Decompose(&map_, keys, values);
+    Traits::Finalize(&map_);
+    map_.clear();
+    is_null_ = true;
+  }
+
+  class ConstMapIterator {
+   public:
+    ConstMapIterator(const typename std::map<KeyStorageType,
+                         ValueStorageType>::const_iterator& it)
+        : it_(it) {}
+
+    KeyConstRefType GetKey() {
+      return Traits::GetKey(it_);
+    }
+    ValueConstRefType GetValue() {
+      return Traits::GetValue(it_);
+    }
+
+    ConstMapIterator& operator++() {
+      it_++;
+      return *this;
+    }
+    bool operator!=(const ConstMapIterator& rhs) const {
+      return it_ != rhs.it_;
+    }
+    bool operator==(const ConstMapIterator& rhs) const {
+      return it_ == rhs.it_;
+    }
+
+   private:
+    typename std::map<KeyStorageType, ValueStorageType>::const_iterator it_;
+  };
+
+  // Provide read-only iteration over map members.
+  ConstMapIterator begin() const { return ConstMapIterator(map_.begin()); }
+  ConstMapIterator end() const { return ConstMapIterator(map_.end()); }
+
+  ConstMapIterator find(KeyForwardType key) const {
+    return ConstMapIterator(map_.find(key));
+  }
+
+ private:
+  typedef std::map<KeyStorageType, ValueStorageType> Map::*Testable;
+
+ public:
+  operator Testable() const { return is_null_ ? 0 : &Map::map_; }
+
+ private:
+  void Take(Map* other) {
+    reset();
+    Swap(other);
+  }
+
+  std::map<KeyStorageType, ValueStorageType> map_;
+  bool is_null_;
+};
+
+template <typename MojoKey, typename MojoValue,
+          typename STLKey, typename STLValue>
+struct TypeConverter<Map<MojoKey, MojoValue>, std::map<STLKey, STLValue> > {
+  static Map<MojoKey, MojoValue> Convert(
+      const std::map<STLKey, STLValue>& input) {
+    Map<MojoKey, MojoValue> result;
+    for (auto& pair : input) {
+      result.insert(TypeConverter<MojoKey, STLKey>::Convert(pair.first),
+                    TypeConverter<MojoValue, STLValue>::Convert(pair.second));
+    }
+    return result.Pass();
+  }
+};
+
+namespace internal {
+
+template <typename MojoKey, typename MojoValue,
+          typename STLKey, typename STLValue>
+class MapTypeConverterCallback {

[yzshen1, 2014/10/03 18:03:38]

What is this for? I didn't see any usage of it.

[Elliot Glaysher, 2014/10/03 21:11:49]

Stray mark. I previously tried a templated Iterate() member function instead of
building my own iterator class. This was a Bad Item[tm] and this was a remnant
of that approach.

+ public:
+  MapTypeConverterCallback(std::map<STLKey, STLValue>* result_in)
+      : result(result_in) {}
+
+  void operator()(const MojoKey& key, const MojoValue& value) {
+    result->insert(std::make_pair(
+        TypeConverter<STLKey, MojoKey>::Convert(key),
+        TypeConverter<STLValue, MojoValue>::Convert(value)));
+  }
+
+ private:
+  std::map<STLKey, STLValue>* result;
+};
+
+}  // namespace internal
+
+template <typename MojoKey, typename MojoValue,
+          typename STLKey, typename STLValue>
+struct TypeConverter<std::map<STLKey, STLValue>, Map<MojoKey, MojoValue> > {
+  static std::map<STLKey, STLValue> Convert(
+      const Map<MojoKey, MojoValue>& input) {
+    std::map<STLKey, STLValue> result;
+    if (!input.is_null()) {
+      for (auto it = input.begin(); it != input.end(); ++it) {
+        result.insert(std::make_pair(
+            TypeConverter<STLKey, MojoKey>::Convert(it.GetKey()),
+            TypeConverter<STLValue, MojoValue>::Convert(it.GetValue())));
+      }
+    }
+    return result;
+  }
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_MAP_H_