ptr.h

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/*
 * Copyright (c) 2005,2006 INRIA
 *
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
 */
 
#ifndef PTR_H
#define PTR_H
 
#include "assert.h"
 
#include <iostream>
#include <stdint.h>
#include <type_traits>
 
/**
 * @file
 * @ingroup ptr
 * ns3::Ptr smart pointer declaration and implementation.
 */
 
namespace ns3
{
 
/**
 * @ingroup core
 * @defgroup ptr Smart Pointer
 * @brief Heap memory management.
 *
 * See \ref ns3::Ptr for implementation details.
 *
 * See \ref main-ptr.cc for example usage.
 */
/**
 * @ingroup ptr
 *
 * @brief Smart pointer class similar to \c boost::intrusive_ptr.
 *
 * This smart-pointer class assumes that the underlying
 * type provides a pair of \c Ref() and \c Unref() methods which are
 * expected to increment and decrement the internal reference count
 * of the object instance.  You can add \c Ref() and \c Unref()
 * to a class simply by inheriting from ns3::SimpleRefCount<>
 * using the CRTP (`class Foo : public SimpleRefCount<Foo>`)
 *
 * This implementation allows you to manipulate the smart pointer
 * as if it was a normal pointer: you can test if it is non-null,
 * compare it to other pointers of the same type, etc.
 *
 * It is possible to extract the raw pointer from this
 * smart pointer with the GetPointer() and PeekPointer() methods.
 *
 * If you want to store a `new Object()` into a smart pointer,
 * we recommend you to use the CreateObject<>() template function
 * to create the Object and store it in a smart pointer to avoid
 * memory leaks. These functions are really small convenience
 * functions and their goal is just is save you a small
 * bit of typing.  If the Object does not inherit from Object
 * (or ObjectBase) there is also a convenience wrapper Create<>()
 *
 * @tparam T \explicit The type of the underlying object.
 */
template <typename T>
class Ptr
{
  private:
    /** The pointer. */
    T* m_ptr;
 
    /** Interoperate with const instances. */
    friend class Ptr<const T>;
 
    /**
     * Get a permanent pointer to the underlying object.
     *
     * The underlying refcount is incremented prior
     * to returning to the caller so the caller is
     * responsible for calling Unref himself.
     *
     * @tparam U \deduced The actual type of the argument and return pointer.
     * @param [in] p Smart pointer
     * @return The pointer managed by this smart pointer.
     */
    template <typename U>
    friend U* GetPointer(const Ptr<U>& p);
    /**
     * Get a temporary pointer to the underlying object.
     *
     * The underlying refcount is not incremented prior
     * to returning to the caller so the caller is not
     * responsible for calling Unref himself.
     *
     * @tparam U \deduced The actual type of the argument and return pointer.
     * @param [in] p Smart pointer
     * @return The pointer managed by this smart pointer.
     */
    template <typename U>
    friend U* PeekPointer(const Ptr<U>& p);
 
    /** Mark this as a a reference by incrementing the reference count. */
    inline void Acquire() const;
 
  public:
    /** Create an empty smart pointer */
    Ptr();
    /**
     * Create a smart pointer which points to the object pointed to by
     * the input raw pointer ptr. This method creates its own reference
     * to the pointed object. The caller is responsible for Unref()'ing
     * its own reference, and the smart pointer will eventually do the
     * same, so that object is deleted if no more references to it
     * remain.
     *
     * @param [in] ptr Raw pointer to manage
     */
    Ptr(T* ptr);
    /**
     * Create a smart pointer which points to the object pointed to by
     * the input raw pointer ptr.
     *
     * @param [in] ptr Raw pointer to manage
     * @param [in] ref if set to true, this method calls Ref, otherwise,
     *        it does not call Ref.
     */
    Ptr(T* ptr, bool ref);
    /**
     * Copy by referencing the same underlying object.
     *
     * @param [in] o The other Ptr instance.
     */
    Ptr(const Ptr& o);
    /**
     * Copy, removing \c const qualifier.
     *
     * @tparam U \deduced The type underlying the Ptr being copied.
     * @param [in] o The Ptr to copy.
     */
    template <typename U>
    Ptr(const Ptr<U>& o);
    /** Destructor. */
    ~Ptr();
    /**
     * Assignment operator by referencing the same underlying object.
     *
     * @param [in] o The other Ptr instance.
     * @return A reference to self.
     */
    Ptr<T>& operator=(const Ptr& o);
    /**
     * An rvalue member access.
     * @returns A pointer to the underlying object.
     */
    T* operator->() const;
    /**
     * An lvalue member access.
     * @returns A pointer to the underlying object.
     */
    T* operator->();
    /**
     * A \c const dereference.
     * @returns A pointer to the underlying object.
     */
    T& operator*() const;
    /**
     * A  dereference.
     * @returns A pointer to the underlying object.
     */
    T& operator*();
 
    /**
     * Test for non-NULL pointer.
     *
     * This enables simple pointer checks like
     * @code
     *   Ptr<...> p = ...;
     *   if (p) ...
     *   if (!p) ...
     * @endcode
     *
     * The same construct works in the NS_ASSERT... and NS_ABORT... macros.
     *
     * @note Explicit tests against `0`, `NULL` or `nullptr` are not supported.
     * All these cases will fail to compile:
     * @code
     *   if (p != nullptr {...}    // Should be `if (p)`
     *   if (p != NULL)   {...}
     *   if (p != 0)      {...}
     *
     *   if (p == nullptr {...}    // Should be `if (!p)`
     *   if (p == NULL)   {...}
     *   if (p == 0)      {...}
     * @endcode
     * Just use `if (p)` or `if (!p)` as indicated.
     *
     * @note NS_TEST... invocations should be written as follows:
     * @code
     * // p should be non-NULL
     * NS_TEST...NE... (p, nullptr, ...);
     * // p should be NULL
     * NS_TEST...EQ... (p, nullptr, ...);
     * @endcode
     *
     * @note Unfortunately return values are not
     * "contextual conversion expression" contexts,
     * so you need to explicitly cast return values to bool:
     * @code
     * bool f (...)
     * {
     *   Ptr<...> p = ...;
     *   return (bool)(p);
     * }
     * @endcode
     *
     * @returns \c true if the underlying pointer is non-NULL.
     */
    explicit operator bool() const;
};
 
/**
 * @ingroup ptr
 * Create class instances by constructors with varying numbers
 * of arguments and return them by Ptr.
 *
 * This template work for any class \c T derived from ns3::SimpleRefCount
 *
 * @see CreateObject for methods to create derivatives of ns3::Object
 */
/** @{ */
/**
 * @tparam T  \explicit The type of class object to create.
 * @tparam Ts \deduced Types of the constructor arguments.
 * @param  [in] args Constructor arguments.
 * @return A Ptr to the newly created \c T.
 */
template <typename T, typename... Ts>
Ptr<T> Create(Ts&&... args);
 
/** @}*/
 
/**
 * @ingroup ptr
 * Output streamer.
 * @tparam T \deduced The type of the underlying Object.
 * @param [in,out] os The output stream.
 * @param [in] p The Ptr.
 * @returns The stream.
 */
template <typename T>
std::ostream& operator<<(std::ostream& os, const Ptr<T>& p);
 
/**
 * @ingroup ptr
 * Equality operator.
 *
 * This enables code such as
 * @code
 *   Ptr<...> p = ...;
 *   Ptr<...> q = ...;
 *   if (p == q) ...
 * @endcode
 *
 * Note that either \c p or \c q could also be ordinary pointers
 * to the underlying object.
 *
 * @tparam T1 \deduced Type of the object on the lhs.
 * @tparam T2 \deduced Type of the object on the rhs.
 * @param [in] lhs The left operand.
 * @param [in] rhs The right operand.
 * @return \c true if the operands point to the same underlying object.
 */
/** @{ */
template <typename T1, typename T2>
bool operator==(const Ptr<T1>& lhs, T2 const* rhs);
 
template <typename T1, typename T2>
bool operator==(T1 const* lhs, Ptr<T2>& rhs);
 
template <typename T1, typename T2>
bool operator==(const Ptr<T1>& lhs, const Ptr<T2>& rhs);
/**@}*/
 
/**
 * @ingroup ptr
 *  Specialization for comparison to \c nullptr
 * @copydoc operator==(Ptr<T1>const&,Ptr<T2>const&)
 */
template <typename T1, typename T2>
std::enable_if_t<std::is_same_v<T2, std::nullptr_t>, bool> operator==(const Ptr<T1>& lhs, T2 rhs);
 
/**
 * @ingroup ptr
 * Inequality operator.
 *
 * This enables code such as
 * @code
 *   Ptr<...> p = ...;
 *   Ptr<...> q = ...;
 *   if (p != q) ...
 * @endcode
 *
 * Note that either \c p or \c q could also be ordinary pointers
 * to the underlying object.
 *
 * @tparam T1 \deduced Type of the object on the lhs.
 * @tparam T2 \deduced Type of the object on the rhs.
 * @param [in] lhs The left operand.
 * @param [in] rhs The right operand.
 * @return \c true if the operands point to the same underlying object.
 */
/** @{ */
template <typename T1, typename T2>
bool operator!=(const Ptr<T1>& lhs, T2 const* rhs);
 
template <typename T1, typename T2>
bool operator!=(T1 const* lhs, Ptr<T2>& rhs);
 
template <typename T1, typename T2>
bool operator!=(const Ptr<T1>& lhs, const Ptr<T2>& rhs);
/**@}*/
 
/**
 * @ingroup ptr
 * Specialization for comparison to \c nullptr
 * @copydoc operator==(Ptr<T1>const&,Ptr<T2>const&)
 */
template <typename T1, typename T2>
std::enable_if_t<std::is_same_v<T2, std::nullptr_t>, bool> operator!=(const Ptr<T1>& lhs, T2 rhs);
 
/**
 * @ingroup ptr
 * Comparison operator applied to the underlying pointers.
 *
 * @tparam T \deduced The type of the operands.
 * @param [in] lhs The left operand.
 * @param [in] rhs The right operand.
 * @return The comparison on the underlying pointers.
 */
/** @{ */
template <typename T>
bool operator<(const Ptr<T>& lhs, const Ptr<T>& rhs);
template <typename T>
bool operator<(const Ptr<T>& lhs, const Ptr<const T>& rhs);
template <typename T>
bool operator<(const Ptr<const T>& lhs, const Ptr<T>& rhs);
template <typename T>
bool operator<=(const Ptr<T>& lhs, const Ptr<T>& rhs);
template <typename T>
bool operator>(const Ptr<T>& lhs, const Ptr<T>& rhs);
template <typename T>
bool operator>=(const Ptr<T>& lhs, const Ptr<T>& rhs);
/** @} */
 
/**
 * Return a copy of \c p with its stored pointer const casted from
 * \c T2 to \c T1.
 *
 * @tparam T1 \deduced The type to return in a Ptr.
 * @tparam T2 \deduced The type of the underlying object.
 * @param [in] p The original \c const Ptr.
 * @return A non-const Ptr.
 */
template <typename T1, typename T2>
Ptr<T1> const_pointer_cast(const Ptr<T2>& p);
 
// Duplicate of struct CallbackTraits<T> as defined in callback.h
template <typename T>
struct CallbackTraits;
 
/**
 * @ingroup callbackimpl
 *
 * Trait class to convert a pointer into a reference,
 * used by MemPtrCallBackImpl.
 *
 * This is the specialization for Ptr types.
 *
 * @tparam T \deduced The type of the underlying object.
 */
template <typename T>
struct CallbackTraits<Ptr<T>>
{
    /**
     * @param [in] p Object pointer
     * @return A reference to the object pointed to by p
     */
    static T& GetReference(const Ptr<T> p)
    {
        return *PeekPointer(p);
    }
};
 
namespace internal
{
 
// Duplicate of struct EventMemberImplObjTraits<T> as defined in make-event.h
// We repeat it here to declare a specialization on Ptr<T>
// without making this header dependent on make-event.h
template <typename T>
struct EventMemberImplObjTraits;
 
/**
 * @ingroup makeeventmemptr
 * Helper for the MakeEvent functions which take a class method.
 *
 * This is the specialization for Ptr types.
 *
 * @tparam T \deduced The type of the underlying object.
 */
template <typename T>
struct EventMemberImplObjTraits<Ptr<T>>
{
    /**
     * @param [in] p Object pointer
     * @return A reference to the object pointed to by p
     */
    static T& GetReference(Ptr<T> p)
    {
        return *PeekPointer(p);
    }
};
 
} // namespace internal
 
} // namespace ns3
 
namespace ns3
{
 
class Object;
 
/*************************************************
 *  friend non-member function implementations
 ************************************************/
 
template <typename T, typename... Ts>
Ptr<T>
Create(Ts&&... args)
{
    static_assert(!std::is_base_of_v<Object, T>,
                  "Use CreateObject() instead of Create() for Object subclasses");
    return Ptr<T>(new T(std::forward<Ts>(args)...), false);
}
 
template <typename U>
U*
PeekPointer(const Ptr<U>& p)
{
    return p.m_ptr;
}
 
template <typename U>
U*
GetPointer(const Ptr<U>& p)
{
    p.Acquire();
    return p.m_ptr;
}
 
template <typename T>
std::ostream&
operator<<(std::ostream& os, const Ptr<T>& p)
{
    os << PeekPointer(p);
    return os;
}
 
template <typename T1, typename T2>
bool
operator==(const Ptr<T1>& lhs, T2 const* rhs)
{
    return PeekPointer(lhs) == rhs;
}
 
template <typename T1, typename T2>
bool
operator==(T1 const* lhs, Ptr<T2>& rhs)
{
    return lhs == PeekPointer(rhs);
}
 
template <typename T1, typename T2>
bool
operator!=(const Ptr<T1>& lhs, T2 const* rhs)
{
    return PeekPointer(lhs) != rhs;
}
 
template <typename T1, typename T2>
bool
operator!=(T1 const* lhs, Ptr<T2>& rhs)
{
    return lhs != PeekPointer(rhs);
}
 
template <typename T1, typename T2>
bool
operator==(const Ptr<T1>& lhs, const Ptr<T2>& rhs)
{
    return PeekPointer(lhs) == PeekPointer(rhs);
}
 
template <typename T1, typename T2>
bool
operator!=(const Ptr<T1>& lhs, const Ptr<T2>& rhs)
{
    return PeekPointer(lhs) != PeekPointer(rhs);
}
 
template <typename T1, typename T2>
std::enable_if_t<std::is_same_v<T2, std::nullptr_t>, bool>
operator==(const Ptr<T1>& lhs, T2 rhs)
{
    return PeekPointer(lhs) == nullptr;
}
 
template <typename T1, typename T2>
std::enable_if_t<std::is_same_v<T2, std::nullptr_t>, bool>
operator!=(const Ptr<T1>& lhs, T2 rhs)
{
    return PeekPointer(lhs) != nullptr;
}
 
template <typename T>
bool
operator<(const Ptr<T>& lhs, const Ptr<T>& rhs)
{
    return PeekPointer<T>(lhs) < PeekPointer<T>(rhs);
}
 
template <typename T>
bool
operator<(const Ptr<T>& lhs, const Ptr<const T>& rhs)
{
    return PeekPointer<T>(lhs) < PeekPointer<const T>(rhs);
}
 
template <typename T>
bool
operator<(const Ptr<const T>& lhs, const Ptr<T>& rhs)
{
    return PeekPointer<const T>(lhs) < PeekPointer<T>(rhs);
}
 
template <typename T>
bool
operator<=(const Ptr<T>& lhs, const Ptr<T>& rhs)
{
    return PeekPointer<T>(lhs) <= PeekPointer<T>(rhs);
}
 
template <typename T>
bool
operator>(const Ptr<T>& lhs, const Ptr<T>& rhs)
{
    return PeekPointer<T>(lhs) > PeekPointer<T>(rhs);
}
 
template <typename T>
bool
operator>=(const Ptr<T>& lhs, const Ptr<T>& rhs)
{
    return PeekPointer<T>(lhs) >= PeekPointer<T>(rhs);
}
 
/**
 * Cast a Ptr.
 *
 * @tparam T1 \deduced The desired type to cast to.
 * @tparam T2 \deduced The type of the original Ptr.
 * @param [in] p The original Ptr.
 * @return The result of the cast.
 */
/** @{ */
template <typename T1, typename T2>
Ptr<T1>
ConstCast(const Ptr<T2>& p)
{
    return Ptr<T1>(const_cast<T1*>(PeekPointer(p)));
}
 
template <typename T1, typename T2>
Ptr<T1>
DynamicCast(const Ptr<T2>& p)
{
    return Ptr<T1>(dynamic_cast<T1*>(PeekPointer(p)));
}
 
template <typename T1, typename T2>
Ptr<T1>
StaticCast(const Ptr<T2>& p)
{
    return Ptr<T1>(static_cast<T1*>(PeekPointer(p)));
}
 
/** @} */
 
/**
 * Return a deep copy of a Ptr.
 *
 * @tparam T \deduced The type of the underlying object.
 * @param [in] object The object Ptr to copy.
 * @returns The copy.
 */
/** @{ */
template <typename T>
Ptr<T>
Copy(Ptr<T> object)
{
    Ptr<T> p = Ptr<T>(new T(*PeekPointer(object)), false);
    return p;
}
 
template <typename T>
Ptr<T>
Copy(Ptr<const T> object)
{
    Ptr<T> p = Ptr<T>(new T(*PeekPointer(object)), false);
    return p;
}
 
/** @} */
 
/****************************************************
 *      Member method implementations.
 ***************************************************/
 
template <typename T>
void
Ptr<T>::Acquire() const
{
    if (m_ptr != nullptr)
    {
        m_ptr->Ref();
    }
}
 
template <typename T>
Ptr<T>::Ptr()
    : m_ptr(nullptr)
{
}
 
template <typename T>
Ptr<T>::Ptr(T* ptr)
    : m_ptr(ptr)
{
    Acquire();
}
 
template <typename T>
Ptr<T>::Ptr(T* ptr, bool ref)
    : m_ptr(ptr)
{
    if (ref)
    {
        Acquire();
    }
}
 
template <typename T>
Ptr<T>::Ptr(const Ptr& o)
    : m_ptr(nullptr)
{
    T* ptr = PeekPointer(o);
    if (ptr != nullptr)
    {
        m_ptr = ptr;
        Acquire();
    }
}
 
template <typename T>
template <typename U>
Ptr<T>::Ptr(const Ptr<U>& o)
    : m_ptr(PeekPointer(o))
{
    Acquire();
}
 
template <typename T>
Ptr<T>::~Ptr()
{
    if (m_ptr != nullptr)
    {
        m_ptr->Unref();
    }
}
 
template <typename T>
Ptr<T>&
Ptr<T>::operator=(const Ptr& o)
{
    if (&o == this)
    {
        return *this;
    }
    if (m_ptr != nullptr)
    {
        m_ptr->Unref();
    }
    m_ptr = o.m_ptr;
    Acquire();
    return *this;
}
 
template <typename T>
T*
Ptr<T>::operator->()
{
    NS_ASSERT_MSG(m_ptr, "Attempted to dereference zero pointer");
    return m_ptr;
}
 
template <typename T>
T*
Ptr<T>::operator->() const
{
    NS_ASSERT_MSG(m_ptr, "Attempted to dereference zero pointer");
    return m_ptr;
}
 
template <typename T>
T&
Ptr<T>::operator*() const
{
    NS_ASSERT_MSG(m_ptr, "Attempted to dereference zero pointer");
    return *m_ptr;
}
 
template <typename T>
T&
Ptr<T>::operator*()
{
    NS_ASSERT_MSG(m_ptr, "Attempted to dereference zero pointer");
    return *m_ptr;
}
 
template <typename T>
Ptr<T>::operator bool() const
{
    return m_ptr != nullptr;
}
 
} // namespace ns3
 
/****************************************************
 *      Global Functions (outside namespace ns3)
 ***************************************************/
 
/**
 * @ingroup ptr
 * Hashing functor taking a `Ptr` and returning a @c std::size_t.
 * For use with `unordered_map` and `unordered_set`.
 *
 * @note When a `Ptr` is used in a container the lifetime of the underlying
 * object is at least as long as the container.  In other words,
 * you need to remove the object from the container when you are done with
 * it, otherwise the object will persist until the container itself is
 * deleted.
 *
 * @tparam T \deduced The type held by the `Ptr`
 */
template <class T>
struct std::hash<ns3::Ptr<T>>
{
    /**
     * The functor.
     * @param p The `Ptr` value to hash.
     * @return the hash
     */
    std::size_t operator()(ns3::Ptr<T> p) const
    {
        return std::hash<const T*>()(ns3::PeekPointer(p));
    }
};
 
#endif /* PTR_H */