itkSmartPointer.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 itkSmartPointer_h
#define itkSmartPointer_h
 
#include <iostream>
#include <utility>
#include <type_traits>
#include "itkConfigure.h"
 
 
namespace itk
{
template <typename TObjectType>
class SmartPointer
{
public:
  using ObjectType = TObjectType;
 
  template <typename T>
  using EnableIfConvertible = typename std::enable_if<std::is_convertible_v<T *, TObjectType *>>;

  constexpr SmartPointer() noexcept = default;

  SmartPointer(const SmartPointer & p) noexcept
    : m_Pointer(p.m_Pointer)
  {
    this->Register();
  }

  constexpr SmartPointer(std::nullptr_t) noexcept {}

  template <typename T, typename = typename EnableIfConvertible<T>::type>
  SmartPointer(const SmartPointer<T> & p) noexcept
    : m_Pointer(p.m_Pointer)
  {
    this->Register();
  }

  SmartPointer(SmartPointer<ObjectType> && p) noexcept
    : m_Pointer(p.m_Pointer)
  {
    p.m_Pointer = nullptr;
  }

  template <typename T, typename = typename EnableIfConvertible<T>::type>
  SmartPointer(SmartPointer<T> && p) noexcept
    : m_Pointer(p.m_Pointer)
  {
    p.m_Pointer = nullptr;
  }

  SmartPointer(ObjectType * p) noexcept
    : m_Pointer(p)
  {
    this->Register();
  }

  ~SmartPointer() { this->UnRegister(); }

  ObjectType *
  operator->() const noexcept
  {
    return m_Pointer;
  }
 
  ObjectType &
  operator*() const noexcept
  {
    return *m_Pointer;
  }
 
  explicit
  operator bool() const noexcept
  {
    return m_Pointer != nullptr;
  }

  operator ObjectType *() const noexcept { return m_Pointer; }

  [[nodiscard]] bool
  IsNotNull() const noexcept
  {
    return m_Pointer != nullptr;
  }

  [[nodiscard]] bool
  IsNull() const noexcept
  {
    return m_Pointer == nullptr;
  }
 

  [[nodiscard]] ObjectType *
  GetPointer() const noexcept
  {
    return m_Pointer;
  }

  [[nodiscard]] ObjectType *
  get() const noexcept
  {
    return m_Pointer;
  }
 

  // cppcheck-suppress operatorEqVarError
  SmartPointer &
  operator=(SmartPointer r) noexcept
  {
    // The Copy-Swap idiom is used, with the implicit copy from the
    // value-based argument r (intentionally not reference). If a move
    // is requested it will be moved into r with the move constructor.
    this->Swap(r);
    return *this;
  }
 
  SmartPointer &
  operator=(std::nullptr_t) noexcept
  {
    this->UnRegister();
    this->m_Pointer = nullptr;
    return *this;
  }


  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;
  }
 
#if !defined(ITK_LEGACY_REMOVE)
  void
  swap(SmartPointer & other) noexcept
  {
    this->Swap(other);
  }
#endif
 
  void
  Swap(SmartPointer & other) noexcept
  {
    ObjectType * tmp = this->m_Pointer;
    this->m_Pointer = other.m_Pointer;
    other.m_Pointer = tmp;
  }
 
private:
  ObjectType * m_Pointer{ nullptr };
 
  template <typename T>
  friend class SmartPointer;
 
  void
  Register() noexcept
  {
    if (m_Pointer)
    {
      m_Pointer->Register();
    }
  }
 
  void
  UnRegister() noexcept
  {
    if (m_Pointer)
    {
      m_Pointer->UnRegister();
    }
  }
};
 

template <class T, class TU>
bool
operator==(const SmartPointer<T> & l, const SmartPointer<TU> & r) noexcept
{
  return l.GetPointer() == r.GetPointer();
}
template <class T>
bool
operator==(const SmartPointer<T> & l, std::nullptr_t) noexcept
{
  return l.GetPointer() == nullptr;
}
template <class T>
bool
operator==(std::nullptr_t, const SmartPointer<T> & r) noexcept
{
  return nullptr == r.GetPointer();
}

template <class T, class TU>
bool
operator!=(const SmartPointer<T> & l, const SmartPointer<TU> & r) noexcept
{
  return l.GetPointer() != r.GetPointer();
}
template <class T>
bool
operator!=(const SmartPointer<T> & l, std::nullptr_t) noexcept
{
  return l.GetPointer() != nullptr;
}
template <class T>
bool
operator!=(std::nullptr_t, const SmartPointer<T> & r) noexcept
{
  return nullptr != r.GetPointer();
}


template <class T, class TU>
bool
operator<(const SmartPointer<T> & l, const SmartPointer<TU> & r) noexcept
{
  return l.GetPointer() < r.GetPointer();
}

template <class T, class TU>
bool
operator>(const SmartPointer<T> & l, const SmartPointer<TU> & r) noexcept
{
  return l.GetPointer() > r.GetPointer();
}

template <class T, class TU>
bool
operator<=(const SmartPointer<T> & l, const SmartPointer<TU> & r) noexcept
{
  return l.GetPointer() <= r.GetPointer();
}

template <class T, class TU>
bool
operator>=(const SmartPointer<T> & l, const SmartPointer<TU> & r) noexcept
{
  return l.GetPointer() >= r.GetPointer();
}
 
template <typename T>
std::ostream &
operator<<(std::ostream & os, const SmartPointer<T> p)
{
  p.Print(os);
  return os;
}
 
template <typename T>
inline void
swap(SmartPointer<T> & a, SmartPointer<T> & b) noexcept
{
  a.Swap(b);
}
 
} // end namespace itk
 
#endif