src/misc/countedptr.hpp

   1 /* $Id: countedptr.hpp 24900 2013-01-08 22:46:42Z planetmaker $ */
   2
   3 /*
   4  * This file is part of OpenTTD.
   5  * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
   6  * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   7  * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
   8  */
   9
  10 /** @file countedptr.hpp CCountedPtr - smart pointer implementation. */
  11
  12 #ifndef COUNTEDPTR_HPP
  13 #define COUNTEDPTR_HPP
  14
  15 /**
  16  * CCountedPtr - simple reference counting smart pointer.
  17  *
  18  *     One of the standard ways how to maintain object's lifetime.
  19  *
  20  *     See http://ootips.org/yonat/4dev/smart-pointers.html for more
  21  *   general info about smart pointers.
  22  *
  23  *     This class implements ref-counted pointer for objects/interfaces that
  24  *   support AddRef() and Release() methods.
  25  */
  26 template <class Tcls_>
  27 class CCountedPtr {
  28         /** redefine the template argument to make it visible for derived classes */
  29 public:
  30         typedef Tcls_ Tcls;
  31
  32 protected:
  33         /** here we hold our pointer to the target */
  34         Tcls *m_pT;
  35
  36 public:
  37         /** default (nullptr) construct or construct from a raw pointer */
  38         inline CCountedPtr(Tcls *pObj = nullptr) : m_pT(pObj)
  39         {
  40                 AddRef();
  41         }
  42
  43         /** copy constructor (invoked also when initializing from another smart ptr) */
  44         inline CCountedPtr(const CCountedPtr &src) : m_pT(src.m_pT)
  45         {
  46                 AddRef();
  47         }
  48
  49         /** destructor releasing the reference */
  50         inline ~CCountedPtr()
  51         {
  52                 Release();
  53         }
  54
  55 protected:
  56         /** add one ref to the underlaying object */
  57         inline void AddRef()
  58         {
  59                 if (m_pT != nullptr) m_pT->AddRef();
  60         }
  61
  62 public:
  63         /** release smart pointer (and decrement ref count) if not null */
  64         inline void Release()
  65         {
  66                 if (m_pT != nullptr) {
  67                         Tcls *pT = m_pT;
  68                         m_pT = nullptr;
  69                         pT->Release();
  70                 }
  71         }
  72
  73         /** dereference of smart pointer - const way */
  74         inline const Tcls *operator->() const
  75         {
  76                 assert(m_pT != nullptr);
  77                 return m_pT;
  78         }
  79
  80         /** dereference of smart pointer - non const way */
  81         inline Tcls *operator->()
  82         {
  83                 assert(m_pT != nullptr);
  84                 return m_pT;
  85         }
  86
  87         /** raw pointer casting operator - const way */
  88         inline operator const Tcls*() const
  89         {
  90                 assert(m_pT == nullptr);
  91                 return m_pT;
  92         }
  93
  94         /** raw pointer casting operator - non-const way */
  95         inline operator Tcls*()
  96         {
  97                 return m_pT;
  98         }
  99
 100         /** operator & to support output arguments */
 101         inline Tcls** operator&()
 102         {
 103                 assert(m_pT == nullptr);
 104                 return &m_pT;
 105         }
 106
 107         /** assignment operator from raw ptr */
 108         inline CCountedPtr& operator=(Tcls *pT)
 109         {
 110                 Assign(pT);
 111                 return *this;
 112         }
 113
 114         /** assignment operator from another smart ptr */
 115         inline CCountedPtr& operator=(const CCountedPtr &src)
 116         {
 117                 Assign(src.m_pT);
 118                 return *this;
 119         }
 120
 121         /** assignment operator helper */
 122         inline void Assign(Tcls *pT);
 123
 124         /** one way how to test for nullptr value */
 125         inline bool IsNull() const
 126         {
 127                 return m_pT == nullptr;
 128         }
 129
 130         /** another way how to test for nullptr value */
 131         //inline bool operator == (const CCountedPtr &sp) const {return m_pT == sp.m_pT;}
 132
 133         /** yet another way how to test for nullptr value */
 134         //inline bool operator != (const CCountedPtr &sp) const {return m_pT != sp.m_pT;}
 135
 136         /** assign pointer w/o incrementing ref count */
 137         inline void Attach(Tcls *pT)
 138         {
 139                 Release();
 140                 m_pT = pT;
 141         }
 142
 143         /** detach pointer w/o decrementing ref count */
 144         inline Tcls *Detach()
 145         {
 146                 Tcls *pT = m_pT;
 147                 m_pT = nullptr;
 148                 return pT;
 149         }
 150 };
 151
 152 template <class Tcls_>
 153 inline void CCountedPtr<Tcls_>::Assign(Tcls *pT)
 154 {
 155         /* if they are the same, we do nothing */
 156         if (pT != m_pT) {
 157                 if (pT != nullptr) pT->AddRef();        // AddRef new pointer if any
 158                 Tcls *pTold = m_pT;                  // save original ptr
 159                 m_pT = pT;                           // update m_pT to new value
 160                 if (pTold != nullptr) pTold->Release(); // release old ptr if any
 161         }
 162 }
 163
 164 /**
 165  * Adapter wrapper for CCountedPtr like classes that can't be used directly by stl
 166  * collections as item type. For example CCountedPtr has overloaded operator & which
 167  * prevents using CCountedPtr in stl collections (i.e. std::list<CCountedPtr<MyType> >)
 168  */
 169 template <class T> struct AdaptT {
 170         T m_t;
 171
 172         /** construct by wrapping the given object */
 173         AdaptT(const T &t)
 174                 : m_t(t)
 175         {}
 176
 177         /** assignment operator */
 178         T& operator = (const T &t)
 179         {
 180                 m_t = t;
 181                 return t;
 182         }
 183
 184         /** type-cast operator (used when AdaptT is used instead of T) */
 185         operator T& ()
 186         {
 187                 return m_t;
 188         }
 189
 190         /** const type-cast operator (used when AdaptT is used instead of const T) */
 191         operator const T& () const
 192         {
 193                 return m_t;
 194         }
 195 };
 196
 197 /**
 198  * Simple counted object. Use it as base of your struct/class if you want to use
 199  *  basic reference counting. Your struct/class will destroy and free itself when
 200  *  last reference to it is released (using Release() method). The initial reference
 201  *  count (when it is created) is zero (don't forget AddRef() at least one time if
 202  *  not using CCountedPtr<T>.
 203  *
 204  *  @see misc/countedobj.cpp for implementation.
 205  */
 206 struct SimpleCountedObject {
 207         int32 m_ref_cnt;
 208
 209         SimpleCountedObject()
 210                 : m_ref_cnt(0)
 211         {}
 212
 213         virtual ~SimpleCountedObject()
 214         {}
 215
 216         virtual int32 AddRef();
 217         virtual int32 Release();
 218         virtual void FinalRelease() {};
 219 };
 220
 221 #endif /* COUNTEDPTR_HPP */