text: // Copyright (c) 2012 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 BASE_SUPPORTS_USER_DATA_H_
  #define BASE_SUPPORTS_USER_DATA_H_
  
  #include <map>
  
  #include "base/base_export.h"
  #include "base/memory/linked_ptr.h"
  #include "base/memory/ref_counted.h"
  
  namespace base {
  
  // This is a helper for classes that want to allow users to stash random data by
  // key. At destruction all the objects will be destructed.
  class BASE_EXPORT SupportsUserData {
   public:
    SupportsUserData();
    virtual ~SupportsUserData();
  
    // Derive from this class and add your own data members to associate extra
    // information with this object. Use GetUserData(key) and SetUserData()
    class BASE_EXPORT Data {
     public:
      virtual ~Data() {}
    };
  
    // The user data allows the clients to associate data with this object.
    // Multiple user data values can be stored under different keys.
    // This object will TAKE OWNERSHIP of the given data pointer, and will
    // delete the object if it is changed or the object is destroyed.
    Data* GetUserData(const void* key) const;
    void SetUserData(const void* key, Data* data);
  
   private:
    typedef std::map<const void*, linked_ptr<Data> > DataMap;
  
    // Externally-defined data accessible by key
    DataMap user_data_;
  
    DISALLOW_COPY_AND_ASSIGN(SupportsUserData);
  };
  
  // Adapter class that releases a refcounted object when the
  // SupportsUserData::Data object is deleted.
  template <typename T>
  class UserDataAdapter : public base::SupportsUserData::Data {
   public:
    static T* Get(SupportsUserData* supports_user_data, const char* key) {
     UserDataAdapter* data =
        static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key));
      return static_cast<T*>(data->object_.get());
    }
  
    UserDataAdapter(T* object) : object_(object) {}
    T* release() { return object_.release(); }
  
   private:
    scoped_refptr<T> object_;
  
    DISALLOW_COPY_AND_ASSIGN(UserDataAdapter);
  };
  
  }  // namespace base
  
  #endif  // BASE_SUPPORTS_USER_DATA_H_
  