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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
{
/** \class WeakPointer
* \brief Implements a weak reference to an object.
*
* WeakPointer implements a weak reference to an object. A natural
* interface to the class is defined by operator -> (and *) among others.
* WeakPointer is really nothing more than a standard pointer. It is used
* to call attention to the fact that it does not adjust the reference
* count of an object like SmartPointer does. WeakPointer is used internally
* to Insight to manage (break) reference counting loops. At some point,
* an object may keep track of how many objects hold weak references to
* itself. In all cases, however, an outstanding weak reference will not
* keep an object from destructing.
*
* \ingroup ITKSystemObjects
* \ingroup DataAccess
* \ingroup ITKCommon
*/
template <typename TObjectType>
class WeakPointer
{
public:
/** Extract information from template parameter. */
using ObjectType = TObjectType;
/** Explicitly-defaulted default-constructor.
* \note The other five "special member functions" (copy-constructor,
* copy-assignment operator, move-constructor, move-assignment operator,
* and destructor) are defaulted implicitly, following the C++ "Rule of Zero".
*/
WeakPointer() = default;
/** Constructor, converting from `nullptr`. */
WeakPointer(std::nullptr_t) {}
/** Constructor to pointer p. */
WeakPointer(ObjectType * p)
: m_Pointer(p)
{}
/** Overload operator ->. */
ObjectType * operator->() const { return m_Pointer; }
/** Return pointer to object. */
operator ObjectType *() const { return m_Pointer; }
/** Template comparison operators. */
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
/** Access function to pointer. */
ObjectType *
GetPointer() const
{
return m_Pointer;
}
/** Test if the pointer is not NULL. */
bool
IsNotNull() const
{
return m_Pointer != nullptr;
}
/** Test if the pointer is NULL. */
bool
IsNull() const
{
return m_Pointer == nullptr;
}
/** Comparison of pointers. Less than comparison. */
bool
operator<(const WeakPointer & r) const
{
return (void *)m_Pointer < (void *)r.m_Pointer;
}
/** Comparison of pointers. Greater than comparison. */
bool
operator>(const WeakPointer & r) const
{
return (void *)m_Pointer > (void *)r.m_Pointer;
}
/** Comparison of pointers. Less than or equal to comparison. */
bool
operator<=(const WeakPointer & r) const
{
return (void *)m_Pointer <= (void *)r.m_Pointer;
}
/** Comparison of pointers. Greater than or equal to comparison. */
bool
operator>=(const WeakPointer & r) const
{
return (void *)m_Pointer >= (void *)r.m_Pointer;
}
/** Function to print object pointed to. */
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:
/** The pointer to the object referred to by this smart pointer. */
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
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