CowPtr.h

 
#pragma once
 
#if defined(CowPtr_RECURSES)
#error Recursive header files inclusion detected in CowPtr.h
#else // defined(CowPtr_RECURSES)
#define CowPtr_RECURSES
 
#if !defined CowPtr_h
#define CowPtr_h
 
// Inclusions
#include <iostream>
#include <type_traits>
#include "DGtal/base/Common.h"
#include "DGtal/base/CountedPtr.h"
 
namespace DGtal
{
 
  // template class CowPtr
  template <typename T>
  class CowPtr
  {
    // ----------------------- Standard services ------------------------------
  public:
public:
    typedef T element_type;
 
    explicit CowPtr(T* p = 0) noexcept           : myPtr(p) {}
    // no need for ~CowPtr - the CountedPtr takes care of everything.
    CowPtr(const CowPtr& r) noexcept             : myPtr(r.myPtr) {}
    CowPtr(const CountedPtr<T> & r, bool /* unused */ )    : myPtr( r ) {}
    CowPtr& operator=(const CowPtr& r)
    {
        if (this != &r)
            myPtr = r.myPtr;
        return *this;
    }
 
 
    const T& operator*()    const noexcept   {return *myPtr;}
    const T* operator->()   const noexcept   {return myPtr.get();}
    const T* get()          const noexcept   {return myPtr.get();}
 
    /* The following non-const methods are deactivated if T is a const type.
     * The goal here is to avoid unecessary copies when it is known that
     *   the T object will not be modified.
     *
     * The problem is that C++ uses the non-const methods whenever it's possible
     *   (ie when CowPtr<T> is non-const), even if the full expression doesn't 
     *   modify the object. A solution is to const_cast the CowPtr<T> before
     *   using one of these methods to force the usage of the const versions above.
     *
     * However, in the trivial case when T is a const type, we can simplify this
     *   by deactivating those methods.
     *
     * To do that, we use std::enable_if (see http://en.cppreference.com/w/cpp/types/enable_if )
     *   in the template parameters (it is also possible in the return type or
     *   as a parameter but it will change the signature). It depends on
     *   the constness of T returned by the type trait std::is_const.
     * The `typename U = T` is necessary in order that the SFINAE rule works at the overload
     * resolution step.
     */
    template < typename U = T, typename std::enable_if< ! std::is_const<U>::value >::type* = nullptr >
    T& operator*()                          {copy(); return *myPtr;}
 
    template < typename U = T, typename std::enable_if< ! std::is_const<U>::value >::type* = nullptr >
    T* operator->()                         {copy(); return myPtr.get();}
 
    template < typename U = T, typename std::enable_if< ! std::is_const<U>::value >::type* = nullptr >
    T* get()                                {copy(); return myPtr.get();}
 
    bool operator==( const T* other ) const
    {
      return get() == other;
    }
 
    bool operator!=( const T* other ) const
    {
      return get() != other;
    }
 
 
    unsigned int count() const          { return myPtr.count(); }
    inline T* drop() { return myPtr.drop(); }
    inline bool unique() const noexcept { return myPtr.unique(); }
 
  private:
 
    // ------------------------- Private Datas --------------------------------
  private:
 
    CountedPtr<T> myPtr;
 
    // ------------------------- Internals ------------------------------------
  private:
    void copy()                            // create a new copy of myPtr
    {
        if (!myPtr.unique()) {
            T* old_p = myPtr.get();
            myPtr = CountedPtr<T>(new T(*old_p));
        }
    }
 
 
    // ----------------------- Interface --------------------------------------
  public:
 
    void selfDisplay ( std::ostream & out ) const;
 
    bool isValid() const;
 
    // ------------------------- Protected Datas ------------------------------
  private:
 
    // ------------------------- Hidden services ------------------------------
  protected:
 
 
 
  }; // end of class CowPtr
 
 
  template <typename T>
  std::ostream&
  operator<< ( std::ostream & out, const CowPtr<T> & object );
 
} // namespace DGtal
 
 
// Includes inline functions.
#include "DGtal/base/CowPtr.ih"
 
//                                                                           //
 
#endif // !defined CowPtr_h
 
#undef CowPtr_RECURSES
#endif // else defined(CowPtr_RECURSES)