关于c++:More-Effective-C技术篇要求或禁止对象产生于heap之中

要求对象产生于heap中，意思是须要阻止clients不得应用new以外的办法产生对象。比拟好的办法就是将destructor定义为private，因为constructor的类型太多，所以依然将constructor定义为public。而后定义一个pseudo destructor来调用真正的destructor。示例如下：

class HeapBasedObject {public:  HeapBasedObject() {}  void destroy() const { delete this; } // pseudo destructorprivate:  ~HeapBasedObject() {}};int main(){  //HeapBasedObject h;  HeapBasedObject *ph = new HeapBasedObject;  //delete ph;  ph->destroy();}

禁止对象产生于heap中，则是要让clients不能应用new办法来产生对象。办法就是将operator new和operator delete定义为private。示例如下：

#include <stdlib.h>class NoHeapBasedObject {public:  NoHeapBasedObject() {}  ~NoHeapBasedObject() {}private:  static void *operator new(size_t size) {}  static void operator delete(void *ptr) {}};int main(){  NoHeapBasedObject nh;  static NoHeapBasedObject snh;  //NoHeapBasedObject *pnh = new NoHeapBasedObject;}

下例是实现的一个判断某个对象是否位于heap内的基类HeapTracked。

#include <stdlib.h>#include <list>#include <iostream>class HeapTracked {public:  class MissingAddress{}; //地址异样  virtual ~HeapTracked() = 0;  static void *operator new(size_t size);  static void operator delete(void *ptr);  bool isOnHeap() const;private:  typedef const void* RawAddress;  static std::list<RawAddress> addresses;};std::list<HeapTracked::RawAddress> HeapTracked::addresses;HeapTracked::~HeapTracked() {}void* HeapTracked::operator new(size_t size) {  void* memPtr = ::operator new(size); // 获得内存。  addresses.push_front(memPtr); // 将其地址置于list头部。  return memPtr;}void HeapTracked::operator delete(void *ptr) {  auto it = std::find(addresses.begin(), addresses.end(), ptr);  if (it != addresses.end()) {      addresses.erase(it);      ::operator delete(ptr);  } else {      throw MissingAddress();  }}bool HeapTracked::isOnHeap() const {  auto rawAddress = dynamic_cast<const void*>(this);  auto it = std::find(addresses.begin(), addresses.end(), rawAddress);    return it != addresses.end();}class Object: public HeapTracked {public:  Object() {}  ~Object() {}};int main(){  Object o1;  Object* o2 = new Object;  std::cout << "o1 isOnHeap = " << o1.isOnHeap() << std::endl;  std::cout << "o2 isOnHeap = " << o2->isOnHeap() << std::endl;}