mysql-server/sql/memory/ref_ptr.h

/* Copyright (c) 2020, 2024, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

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   as designated in a particular file or component or in included license
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   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
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   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

#ifndef MEMORY_REF_PTR_INCLUDED
#define MEMORY_REF_PTR_INCLUDED

#include <sys/stat.h>
#include <sys/types.h>
#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <tuple>

namespace memory {
/**
  Class that holds the pointer to a variable in a static and
  non-destructible way. The purpose is both to clearly state the ownership
  of the memory being pointed to and to avoid unwanted pointer operations
  (a `delete` on a pointer pointing to a stack memory block, for instance).

  It's a convenience class for clearly stating the ownership of the underlying
  pointer and is used for interface and code clarity.
 */
template <typename T>
class Ref_ptr {
 public:
  /**
    Default class constructor.
   */
  Ref_ptr() = default;
  /**
    Class constructor that receives the reference to be managed.

    @param target The reference to be managed.
   */
  Ref_ptr(T &target);
  /**
    Copy constructor.

    @param rhs The object to copy from.
   */
  Ref_ptr(Ref_ptr<T> const &rhs);
  /**
    Move constructor.

    @param rhs The object to move from.
   */
  Ref_ptr(Ref_ptr<T> &&rhs);
  /**
    Default destructor.
   */
  virtual ~Ref_ptr() = default;

  /**
    Assignment operator to instantiate the reference to be managed.

    @param rhs The reference to be managed.

    @return A reference to `this` object.
   */
  Ref_ptr<T> &operator=(T &rhs);
  /**
    Copy operator.

    @param rhs The object to copy from.

    @return A reference to `this` object.
   */
  Ref_ptr<T> &operator=(Ref_ptr<T> const &rhs);
  /**
    Move operator.

    @param rhs The object to move from.

    @return A reference to `this` object.
   */
  Ref_ptr<T> &operator=(Ref_ptr<T> &&rhs);
  /**
    Negation operator.

    @return `true` if there is no managed reference, `false` otherwise.
   */
  bool operator!() const;
  /**
    Arrow operator to access the underlying object of type `T`.

    @return A pointer to the underlying object of type `T`.
   */
  T *operator->() const;
  /**
    Star operator to access the underlying object of type `T`.

    @return A reference to the underlying object of type `T`.
   */
  T &operator*() const;
  /**
    Resets the managed reference and stops managing any pointer.

    @return A reference to `this` object, for chaining purposes.
   */
  Ref_ptr<T> &reset();
  /**
    Equality to `nullptr` operator.

    @param rhs nullptr value

    @return `true` if the managed reference is not instantiated.
   */
  bool operator==(std::nullptr_t rhs) const;
  /**
    Inequality to `nullptr` operator.

    @param rhs nullptr value

    @return `false` if the managed reference is not instantiated.
   */
  bool operator!=(std::nullptr_t rhs) const;
  /**
    Equality  operator.

    @param rhs The object to compare to.

    @return `true` if the managed reference is the same as one managed by the
            `rhs` object.
   */
  template <typename R>
  bool operator==(memory::Ref_ptr<R> const &rhs) const;
  /**
    Inequality  operator.

    @param rhs The object to compare to.

    @return `true` if the managed reference is not the same as one managed by
            the `rhs` object.
   */
  template <typename R>
  bool operator!=(memory::Ref_ptr<R> const &rhs) const;

 private:
  /** The reference to be managed. */
  T *m_underlying{nullptr};
};
}  // namespace memory

template <typename T>
memory::Ref_ptr<T>::Ref_ptr(T &target) : m_underlying{&target} {}

template <typename T>
memory::Ref_ptr<T>::Ref_ptr(memory::Ref_ptr<T> const &rhs)
    : m_underlying{rhs.m_underlying} {}

template <typename T>
memory::Ref_ptr<T>::Ref_ptr(memory::Ref_ptr<T> &&rhs)
    : m_underlying{rhs.m_underlying} {
  rhs.reset();
}

template <typename T>
memory::Ref_ptr<T> &memory::Ref_ptr<T>::operator=(T &rhs) {
  this->m_underlying = &rhs;
  return (*this);
}

template <typename T>
memory::Ref_ptr<T> &memory::Ref_ptr<T>::operator=(
    memory::Ref_ptr<T> const &rhs) {
  this->m_underlying = rhs.m_underlying;
  return (*this);
}

template <typename T>
memory::Ref_ptr<T> &memory::Ref_ptr<T>::operator=(memory::Ref_ptr<T> &&rhs) {
  this->m_underlying = rhs.m_underlying;
  rhs.reset();
  return (*this);
}

template <typename T>
bool memory::Ref_ptr<T>::operator!() const {
  return this->m_underlying == nullptr;
}

template <typename T>
T &memory::Ref_ptr<T>::operator*() const {
  return *this->m_underlying;
}

template <typename T>
T *memory::Ref_ptr<T>::operator->() const {
  return this->m_underlying;
}

template <typename T>
bool memory::Ref_ptr<T>::operator==(std::nullptr_t) const {
  return this->m_underlying == nullptr;
}

template <typename T>
bool memory::Ref_ptr<T>::operator!=(std::nullptr_t) const {
  return this->m_underlying != nullptr;
}

template <typename T>
template <typename R>
bool memory::Ref_ptr<T>::operator==(memory::Ref_ptr<R> const &rhs) const {
  return this->m_underlying == rhs.m_underlying;
}

template <typename T>
template <typename R>
bool memory::Ref_ptr<T>::operator!=(memory::Ref_ptr<R> const &rhs) const {
  return this->m_underlying != rhs.m_underlying;
}

template <typename T>
memory::Ref_ptr<T> &memory::Ref_ptr<T>::reset() {
  this->m_underlying = nullptr;
  return (*this);
}

#endif  // MEMORY_REF_PTR_INCLUDED