base/supports_user_data.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_SUPPORTS_USER_DATA_H_
   6 #define BASE_SUPPORTS_USER_DATA_H_
   7
   8 #include <map>
   9
  10 #include "base/base_export.h"
  11 #include "base/memory/linked_ptr.h"
  12 #include "base/memory/ref_counted.h"
  13
  14 namespace base {
  15
  16 // This is a helper for classes that want to allow users to stash random data by
  17 // key. At destruction all the objects will be destructed.
  18 class BASE_EXPORT SupportsUserData {
  19  public:
  20   SupportsUserData();
  21
  22   // Derive from this class and add your own data members to associate extra
  23   // information with this object. Alternatively, add this as a public base
  24   // class to any class with a virtual destructor.
  25   class BASE_EXPORT Data {
  26    public:
  27     virtual ~Data() {}
  28   };
  29
  30   // The user data allows the clients to associate data with this object.
  31   // Multiple user data values can be stored under different keys.
  32   // This object will TAKE OWNERSHIP of the given data pointer, and will
  33   // delete the object if it is changed or the object is destroyed.
  34   Data* GetUserData(const void* key) const;
  35   void SetUserData(const void* key, Data* data);
  36   void RemoveUserData(const void* key);
  37
  38  protected:
  39   virtual ~SupportsUserData();
  40
  41  private:
  42   typedef std::map<const void*, linked_ptr<Data> > DataMap;
  43
  44   // Externally-defined data accessible by key.
  45   DataMap user_data_;
  46
  47   DISALLOW_COPY_AND_ASSIGN(SupportsUserData);
  48 };
  49
  50 // Adapter class that releases a refcounted object when the
  51 // SupportsUserData::Data object is deleted.
  52 template <typename T>
  53 class UserDataAdapter : public base::SupportsUserData::Data {
  54  public:
  55   static T* Get(SupportsUserData* supports_user_data, const char* key) {
  56    UserDataAdapter* data =
  57       static_cast<UserDataAdapter*>(supports_user_data->GetUserData(key));
  58     return static_cast<T*>(data->object_.get());
  59   }
  60
  61   UserDataAdapter(T* object) : object_(object) {}
  62   T* release() { return object_.release(); }
  63
  64  private:
  65   scoped_refptr<T> object_;
  66
  67   DISALLOW_COPY_AND_ASSIGN(UserDataAdapter);
  68 };
  69
  70 }  // namespace base
  71
  72 #endif  // BASE_SUPPORTS_USER_DATA_H_