Made return types of various Value::DeepCopy() implementations more specific

base/values.h

 // Copyright (c) 2011 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.
 
 // This file specifies a recursive data storage class called Value intended for
 // storing setting and other persistable data.  It includes the ability to
 // specify (recursive) lists and dictionaries, so it's fairly expressive.
 // However, the API is optimized for the common case, namely storing a
 // hierarchical tree of simple values.  Given a DictionaryValue root, you can
 // easily do things like:
@@ skipping 45 matching lines @@
     TYPE_DICTIONARY,
     TYPE_LIST
   };
 
   virtual ~Value();
 
   // Convenience methods for creating Value objects for various
   // kinds of values without thinking about which class implements them.
   // These can always be expected to return a valid Value*.
   static Value* CreateNullValue();
-  static Value* CreateBooleanValue(bool in_value);
-  static Value* CreateIntegerValue(int in_value);
-  static Value* CreateRealValue(double in_value);
-  static Value* CreateStringValue(const std::string& in_value);
-  static Value* CreateStringValue(const string16& in_value);
+  static FundamentalValue* CreateBooleanValue(bool in_value);
+  static FundamentalValue* CreateIntegerValue(int in_value);
+  static FundamentalValue* CreateRealValue(double in_value);
+  static StringValue* CreateStringValue(const std::string& in_value);
+  static StringValue* CreateStringValue(const string16& in_value);
 
   // This one can return NULL if the input isn't valid.  If the return value
   // is non-null, the new object has taken ownership of the buffer pointer.
   static BinaryValue* CreateBinaryValue(char* buffer, size_t size);
 
   // Returns the type of the value stored by the current Value object.
   // Each type will be implemented by only one subclass of Value, so it's
   // safe to use the ValueType to determine whether you can cast from
   // Value* to (Implementing Class)*.  Also, a Value object never changes
   // its type after construction.
   ValueType GetType() const { return type_; }
 
   // Returns true if the current object represents a given type.
   bool IsType(ValueType type) const { return type == type_; }
 
   // These methods allow the convenient retrieval of settings.
   // If the current setting object can be converted into the given type,
   // the value is returned through the |out_value| parameter and true is
   // returned;  otherwise, false is returned and |out_value| is unchanged.
   virtual bool GetAsBoolean(bool* out_value) const;
   virtual bool GetAsInteger(int* out_value) const;
   virtual bool GetAsReal(double* out_value) const;
   virtual bool GetAsString(std::string* out_value) const;
   virtual bool GetAsString(string16* out_value) const;
   virtual bool GetAsList(ListValue** out_value);
 
   // This creates a deep copy of the entire Value tree, and returns a pointer
   // to the copy.  The caller gets ownership of the copy, of course.
+  //
+  // Subclasses return their own type directly in their overrides;
+  // this works because C++ supports covariant return types.
   virtual Value* DeepCopy() const;
 
   // Compares if two Value objects have equal contents.
   virtual bool Equals(const Value* other) const;
 
   // Compares if two Value objects have equal contents. Can handle NULLs.
   // NULLs are considered equal but different from Value::CreateNullValue().
   static bool Equals(const Value* a, const Value* b);
 
  protected:
@@ skipping 14 matching lines @@
  public:
   explicit FundamentalValue(bool in_value);
   explicit FundamentalValue(int in_value);
   explicit FundamentalValue(double in_value);
   virtual ~FundamentalValue();
 
   // Subclassed methods
   virtual bool GetAsBoolean(bool* out_value) const;
   virtual bool GetAsInteger(int* out_value) const;
   virtual bool GetAsReal(double* out_value) const;
-  virtual Value* DeepCopy() const;
+  virtual FundamentalValue* DeepCopy() const;
   virtual bool Equals(const Value* other) const;
 
  private:
   union {
     bool boolean_value_;
     int integer_value_;
     double real_value_;
   };
 
   DISALLOW_COPY_AND_ASSIGN(FundamentalValue);
 };
 
 class StringValue : public Value {
  public:
   // Initializes a StringValue with a UTF-8 narrow character string.
   explicit StringValue(const std::string& in_value);
 
   // Initializes a StringValue with a string16.
   explicit StringValue(const string16& in_value);
 
   virtual ~StringValue();
 
   // Subclassed methods
   virtual bool GetAsString(std::string* out_value) const;
   virtual bool GetAsString(string16* out_value) const;
-  virtual Value* DeepCopy() const;
+  virtual StringValue* DeepCopy() const;
   virtual bool Equals(const Value* other) const;
 
  private:
   std::string value_;
 
   DISALLOW_COPY_AND_ASSIGN(StringValue);
 };
 
 class BinaryValue: public Value {
  public:
   virtual ~BinaryValue();
 
   // Creates a Value to represent a binary buffer.  The new object takes
   // ownership of the pointer passed in, if successful.
   // Returns NULL if buffer is NULL.
   static BinaryValue* Create(char* buffer, size_t size);
 
   // For situations where you want to keep ownership of your buffer, this
   // factory method creates a new BinaryValue by copying the contents of the
   // buffer that's passed in.
   // Returns NULL if buffer is NULL.
   static BinaryValue* CreateWithCopiedBuffer(const char* buffer, size_t size);
 
   size_t GetSize() const { return size_; }
   char* GetBuffer() { return buffer_; }
   const char* GetBuffer() const { return buffer_; }
 
   // Overridden from Value:
-  virtual Value* DeepCopy() const;
+  virtual BinaryValue* DeepCopy() const;
   virtual bool Equals(const Value* other) const;
 
  private:
   // Constructor is private so that only objects with valid buffer pointers
   // and size values can be created.
   BinaryValue(char* buffer, size_t size);
 
   char* buffer_;
   size_t size_;
 
@@ skipping 124 matching lines @@
     bool operator==(const key_iterator& other) { return itr_ == other.itr_; }
 
    private:
     ValueMap::const_iterator itr_;
   };
 
   key_iterator begin_keys() const { return key_iterator(dictionary_.begin()); }
   key_iterator end_keys() const { return key_iterator(dictionary_.end()); }
 
   // Overridden from Value:
-  virtual Value* DeepCopy() const;
+  virtual DictionaryValue* DeepCopy() const;
   virtual bool Equals(const Value* other) const;
 
  private:
   ValueMap dictionary_;
 
   DISALLOW_COPY_AND_ASSIGN(DictionaryValue);
 };
 
 // This type of Value represents a list of other Value values.
 class ListValue : public Value {
@@ skipping 66 matching lines @@
 
   // Iteration
   ListValue::iterator begin() { return list_.begin(); }
   ListValue::iterator end() { return list_.end(); }
 
   ListValue::const_iterator begin() const { return list_.begin(); }
   ListValue::const_iterator end() const { return list_.end(); }
 
   // Overridden from Value:
   virtual bool GetAsList(ListValue** out_value);
-  virtual Value* DeepCopy() const;
+  virtual ListValue* DeepCopy() const;
   virtual bool Equals(const Value* other) const;
 
  private:
   ValueVector list_;
 
   DISALLOW_COPY_AND_ASSIGN(ListValue);
 };
 
 // This interface is implemented by classes that know how to serialize and
 // deserialize Value objects.
 class ValueSerializer {
  public:
   virtual ~ValueSerializer();
 
   virtual bool Serialize(const Value& root) = 0;
 
   // This method deserializes the subclass-specific format into a Value object.
   // If the return value is non-NULL, the caller takes ownership of returned
   // Value. If the return value is NULL, and if error_code is non-NULL,
   // error_code will be set with the underlying error.
   // If |error_message| is non-null, it will be filled in with a formatted
   // error message including the location of the error if appropriate.
   virtual Value* Deserialize(int* error_code, std::string* error_str) = 0;
 };
 
 #endif  // BASE_VALUES_H_