itkWeakPointer.h

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/*=========================================================================
 *
 *  Copyright NumFOCUS
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         https://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef itkWeakPointer_h
#define itkWeakPointer_h
 
#include "itkMacro.h"
#include <iostream>
 
namespace itk
{
template <typename TObjectType>
class WeakPointer
{
public:
  using ObjectType = TObjectType;
 
  WeakPointer() = default;
 
  WeakPointer(std::nullptr_t) {}
 
  WeakPointer(ObjectType * p)
    : m_Pointer(p)
  {}
 
  ObjectType * operator->() const { return m_Pointer; }
 
  operator ObjectType *() const { return m_Pointer; }
 
  template <typename R>
  bool
  operator==(R r) const
  {
    return (m_Pointer == (ObjectType *)r);
  }
 
#ifndef ITK_EXPERIMENTAL_CXX20_REWRITTEN_UNEQUAL_OPERATOR
  template <typename R>
  bool
  operator!=(R r) const
  {
    return !(this->operator==(r));
  }
#endif
 
  ObjectType *
  GetPointer() const
  {
    return m_Pointer;
  }
 
  bool
  IsNotNull() const
  {
    return m_Pointer != nullptr;
  }
 
  bool
  IsNull() const
  {
    return m_Pointer == nullptr;
  }
 
  bool
  operator<(const WeakPointer & r) const
  {
    return (void *)m_Pointer < (void *)r.m_Pointer;
  }
 
  bool
  operator>(const WeakPointer & r) const
  {
    return (void *)m_Pointer > (void *)r.m_Pointer;
  }
 
  bool
  operator<=(const WeakPointer & r) const
  {
    return (void *)m_Pointer <= (void *)r.m_Pointer;
  }
 
  bool
  operator>=(const WeakPointer & r) const
  {
    return (void *)m_Pointer >= (void *)r.m_Pointer;
  }
 
  ObjectType *
  Print(std::ostream & os) const
  {
    if (this->IsNull())
    {
      os << "(null)";
    }
    else
    {
      // This prints the object pointed to by the pointer
      m_Pointer->Print(os);
    }
    return m_Pointer;
  }
private:
  ObjectType * m_Pointer{ nullptr };
};
 
template <typename T>
std::ostream &
operator<<(std::ostream & os, const WeakPointer<T> p)
{
  p.Print(os);
  return os;
}
} // end namespace itk
 
#endif