Mojo C++ bindings: make mojo::Map<K,V> more friendly with std::map<K,V>.

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 <stddef.h>
 #include <map>
 #include <utility>
@@ skipping 14 matching lines @@
 //     using the insert() method.
 template <typename Key, typename Value>
 class Map {
   MOJO_MOVE_ONLY_TYPE(Map)
 
  public:
   // Map keys cannot be move only classes.
   static_assert(!internal::IsMoveOnlyType<Key>::value,
                 "Map keys cannot be move only types.");
 
-  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;
+  using ConstIterator = typename std::map<Key, Value>::const_iterator;
 
-  typedef typename Traits::ValueStorageType ValueStorageType;
-  typedef typename Traits::ValueRefType ValueRefType;
-  typedef typename Traits::ValueConstRefType ValueConstRefType;
-  typedef typename Traits::ValueForwardType ValueForwardType;
-
-  typedef internal::Map_Data<typename internal::WrapperTraits<Key>::DataType,
-                             typename internal::WrapperTraits<Value>::DataType>
-      Data_;
+  using Data_ =
+      internal::Map_Data<typename internal::WrapperTraits<Key>::DataType,
+                         typename internal::WrapperTraits<Value>::DataType>;
 
   Map() : is_null_(true) {}
 
   // Constructs a non-null Map containing the specified |keys| mapped to the
   // corresponding |values|.
   Map(mojo::Array<Key> keys, mojo::Array<Value> values) : is_null_(false) {
     MOJO_DCHECK(keys.size() == values.size());
-    Traits::InitializeFrom(&map_, std::move(keys), std::move(values));
+    for (size_t i = 0; i < keys.size(); ++i)
+      map_.insert(std::make_pair(keys[i], std::move(values[i])));
   }
 
-  ~Map() { Traits::Finalize(&map_); }
+  ~Map() {}
 
+  Map(std::map<Key, Value>&& other) : map_(std::move(other)), is_null_(false) {}
   Map(Map&& other) : is_null_(true) { Take(&other); }
+
   Map& operator=(Map&& other) {
     Take(&other);
     return *this;
   }
 
   // Copies the contents of some other type of map into a new Map using a
   // TypeConverter. A TypeConverter for std::map to Map is defined below.
   template <typename U>
   static Map From(const U& other) {
     return TypeConverter<Map, U>::Convert(other);
   }
 
   // Copies the contents of the Map into some other type of map. A TypeConverter
   // for Map to std::map is defined below.
   template <typename U>
   U To() const {
     return TypeConverter<U, Map>::Convert(*this);
   }
 
   // Destroys the contents of the Map and leaves it in the null state.
   void reset() {
-    if (!map_.empty()) {
-      Traits::Finalize(&map_);
-      map_.clear();
-    }
+    map_.clear();
     is_null_ = true;
   }
 
   bool is_null() const { return is_null_; }
 
   // Indicates the number of keys in the map.
   size_t size() const { return map_.size(); }
 
   void mark_non_null() { is_null_ = false; }
 
-  // Inserts a key-value pair into the map, moving the value by calling its
-  // Pass() method if it is a move-only type. Like std::map, this does not
-  // insert |value| if |key| is already a member of the map.
-  void insert(KeyForwardType key, ValueForwardType value) {
+  // Inserts a key-value pair into the map. Like std::map, this does not insert
+  // |value| if |key| is already a member of the map.
+  void insert(const Key& key, const Value& value) {
     is_null_ = false;
-    Traits::Insert(&map_, key, value);
+    map_.insert(std::make_pair(key, value));
+  }
+  void insert(const Key& key, Value&& value) {
+    is_null_ = false;
+    map_.insert(std::make_pair(key, std::move(value)));
   }
 
   // Returns a reference to the value associated with the specified key,
   // crashing the process if the key is not present in the map.
-  ValueRefType at(KeyForwardType key) { return Traits::at(&map_, key); }
-  ValueConstRefType at(KeyForwardType key) const {
-    return Traits::at(&map_, key);
-  }
+  Value& at(const Key& key) { return map_.at(key); }
+  const Value& at(const Key& key) const { return map_.at(key); }
 
   // Returns a reference to the value associated with the specified key,
   // creating a new entry if the key is not already present in the map. A
   // newly-created value will be value-initialized (meaning that it will be
   // initialized by the default constructor of the value type, if any, or else
   // will be zero-initialized).
-  ValueRefType operator[](KeyForwardType key) {
+  Value& operator[](const Key& key) {
     is_null_ = false;
-    return Traits::GetOrInsert(&map_, key);
+    return map_[key];
+  }
+
+  // Returns a const reference to the std::map managed by this class. If this
+  // object is null, the return value will be an empty map.
+  const std::map<Key, Value>& storage() const { return map_; }
+
+  // Passes the underlying storage and resets this map to null.
+  //
+  // TODO(yzshen): Consider changing this to a rvalue-ref-qualified conversion
+  // to std::map<Key, Value> after we move to MSVC 2015.
+  std::map<Key, Value> PassStorage() {
+    is_null_ = true;
+    return std::move(map_);
   }
 
   // Swaps the contents of this Map with another Map of the same type (including
   // nullness).
   void Swap(Map<Key, Value>* other) {
     std::swap(is_null_, other->is_null_);
     map_.swap(other->map_);
   }
 
   // Swaps the contents of this Map with an std::map containing keys and values
   // of the same type. Since std::map cannot represent the null state, the
   // std::map will be empty if Map is null. The Map will always be left in a
   // non-null state.
   void Swap(std::map<Key, Value>* other) {
     is_null_ = false;
     map_.swap(*other);
   }
 
   // Removes all contents from the Map and places them into parallel key/value
   // arrays. Each key will be copied from the source to the destination, and
   // values will be copied unless their type is designated move-only, in which
   // case they will be passed by calling their Pass() method. Either way, the
   // Map will be left in a null state.
   void DecomposeMapTo(mojo::Array<Key>* keys, mojo::Array<Value>* values) {
-    Traits::Decompose(&map_, keys, values);
-    Traits::Finalize(&map_);
+    std::vector<Key> key_vector;
+    key_vector.reserve(map_.size());
+    std::vector<Value> value_vector;
+    value_vector.reserve(map_.size());
+
+    for (auto& entry : map_) {
+      key_vector.push_back(entry.first);
+      value_vector.push_back(std::move(entry.second));
+    }
+
     map_.clear();
     is_null_ = true;
+
+    keys->Swap(&key_vector);
+    values->Swap(&value_vector);
   }
 
   // Returns a new Map that contains a copy of the contents of this map.  If the
   // values are of a type that is designated move-only, they will be cloned
   // using the Clone() method of the type. Please note that calling this method
   // will fail compilation if the value type cannot be cloned (which usually
   // means that it is a Mojo handle type or a type that contains Mojo handles).
   Map Clone() const {
     Map result;
     result.is_null_ = is_null_;
     Traits::Clone(map_, &result.map_);
-    return std::move(result);
+    return result;
   }
 
   // Indicates whether the contents of this map are equal to those of another
   // Map (including nullness). Keys are compared by the != operator. Values are
   // compared as follows:
   //   - Map, Array, Struct, or StructPtr values are compared by their Equals()
   //     method.
   //   - ScopedHandleBase-derived types are compared by their handles.
   //   - Values of other types are compared by their "==" operator.
   bool Equals(const Map& other) const {
     if (is_null() != other.is_null())
       return false;
     if (size() != other.size())
       return false;
     auto i = begin();
     auto j = other.begin();
     while (i != end()) {
-      if (i.GetKey() != j.GetKey())
+      if (i->first != j->first)
         return false;
-      if (!internal::ValueTraits<Value>::Equals(i.GetValue(), j.GetValue()))
+      if (!internal::ValueTraits<Value>::Equals(i->second, j->second))
         return false;
       ++i;
       ++j;
     }
     return true;
   }
 
-  // A read-only iterator for Map.
-  class ConstMapIterator {
-   public:
-    ConstMapIterator(
-        const typename std::map<KeyStorageType,
-                                ValueStorageType>::const_iterator& it)
-        : it_(it) {}
-
-    // Returns a const reference to the key and value.
-    KeyConstRefType GetKey() { return Traits::GetKey(it_); }
-    ValueConstRefType GetValue() { return Traits::GetValue(it_); }
-
-    ConstMapIterator& operator*() {
-      return *this;
-    }
-    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 in a way similar to STL
   // collections.
-  ConstMapIterator begin() const { return ConstMapIterator(map_.begin()); }
-  ConstMapIterator end() const { return ConstMapIterator(map_.end()); }
+  ConstIterator begin() const { return map_.begin(); }
+  ConstIterator end() const { return map_.end(); }
 
   // Returns the iterator pointing to the entry for |key|, if present, or else
   // returns end().
-  ConstMapIterator find(KeyForwardType key) const {
-    return ConstMapIterator(map_.find(key));
-  }
+  ConstIterator find(const Key& key) const { return map_.find(key); }
 
  private:
-  typedef std::map<KeyStorageType, ValueStorageType> Map::*Testable;
+  typedef std::map<Key, Value> Map::*Testable;
 
  public:
   // The Map may be used in boolean expressions to determine if it is non-null,
   // but is not implicitly convertible to an actual bool value (which would be
   // dangerous).
   operator Testable() const { return is_null_ ? 0 : &Map::map_; }
 
  private:
+  using Traits =
+      internal::MapTraits<Key, Value, internal::IsMoveOnlyType<Value>::value>;
+
   // Forbid the == and != operators explicitly, otherwise Map will be converted
   // to Testable to do == or != comparison.
   template <typename T, typename U>
   bool operator==(const Map<T, U>& other) const = delete;
   template <typename T, typename U>
   bool operator!=(const Map<T, U>& other) const = delete;
 
   void Take(Map* other) {
     reset();
     Swap(other);
   }
 
-  std::map<KeyStorageType, ValueStorageType> map_;
+  std::map<Key, Value> map_;
   bool is_null_;
 };
 
 // Copies the contents of an std::map to a new Map, optionally changing the
 // types of the keys and values along the way using TypeConverter.
 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;
     result.mark_non_null();
     for (auto& pair : input) {
       result.insert(TypeConverter<MojoKey, STLKey>::Convert(pair.first),
                     TypeConverter<MojoValue, STLValue>::Convert(pair.second));
     }
-    return std::move(result);
+    return result;
   }
 };
 
 // Copies the contents of a Map to an std::map, optionally changing the types of
 // the keys and values along the way using TypeConverter.
 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())));
+            TypeConverter<STLKey, MojoKey>::Convert(it->first),
+            TypeConverter<STLValue, MojoValue>::Convert(it->second)));
       }
     }
     return result;
   }
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_MAP_H_