cpp-descriptive-pointers/copy_ptr.hpp

//
//  copy_ptr.hpp
//  pointers
//
//  Created by Sam Jaffe on 12/6/16.
//

#pragma once

#include <functional>
#include <memory>

#include "pointer_fwd.hpp"

namespace detail {
  template <typename T>
  T * copy_ptr_from_ptr(T * ptr) {
    return ptr ? new T(*ptr) : nullptr;
  }
}

template <typename T, T*(*Copy)(T*) = &detail::copy_ptr_from_ptr<T> >
class copy_ptr {
public:
  using element_type = T;
  using pointer = element_type *;
  using reference = element_type &;
  
  copy_ptr() : _ptr(nullptr) {}
  copy_ptr(P const & p) = delete;
  copy_ptr(P && p) : _ptr(std::move(p)) {}
  copy_ptr(copy_ptr const & other) : _ptr(Copy(other._ptr)) {}
  copy_ptr(copy_ptr &&) = default;
  
  template <typename Y>
  explicit operator copy_ptr<Y>() const {
    return Copy(_ptr);
  }
  
  ~copy_ptr() { delete _ptr; }
  
  copy_ptr & operator=(copy_ptr const & other) {
    swap(copy_ptr{other});
    return *this;
  }
  copy_ptr & operator=(copy_ptr &&) = default;
  
  operator bool() const {
    return static_cast<bool>(_ptr);
  }
  
  pointer get() const { return _ptr; }
  pointer operator->() const { return get(); }
  reference operator*() const { return *get(); }
private:
  P _ptr;
};

template <typename T, typename U>
bool operator==(copy_ptr<T> const&lhs, copy_ptr<U> const&rhs) {
  return lhs.get() == rhs.get();
}

template <typename T, typename U>
bool operator!=(copy_ptr<T> const&lhs, copy_ptr<U> const&rhs) {
  return !(lhs == rhs);
}

template <typename T, typename U>
bool operator< (copy_ptr<T> const&lhs, copy_ptr<U> const&rhs) {
  typedef typename std::common_type<
  typename copy_ptr<T>::pointer,
  typename copy_ptr<U>::pointer>::type V;
  return std::less<V>(lhs.get(), rhs.get());
}

template <typename T, typename U>
bool operator> (copy_ptr<T> const&lhs, copy_ptr<U> const&rhs) {
  return rhs < lhs;
}

template <typename T, typename U>
bool operator<=(copy_ptr<T> const&lhs, copy_ptr<U> const&rhs) {
  return !(rhs < lhs);
}

template <typename T, typename U>
bool operator>=(copy_ptr<T> const&lhs, copy_ptr<U> const&rhs) {
  return !(lhs < rhs);
}

template <typename T>
bool operator==(copy_ptr<T> const&lhs, std::nullptr_t) {
  return !lhs;
}

template <typename T>
bool operator==(std::nullptr_t, copy_ptr<T> const&rhs) {
  return !rhs;
}

template <typename T>
bool operator!=(copy_ptr<T> const&lhs, std::nullptr_t) {
  return static_cast<bool>(lhs);
}

template <typename T>
bool operator!=(std::nullptr_t, copy_ptr<T> const&rhs) {
  return static_cast<bool>(rhs);
}

template <typename T>
bool operator< (copy_ptr<T> const&lhs, std::nullptr_t) {
  typedef typename copy_ptr<T>::pointer V;
  return std::less<V>(lhs.get(), nullptr);
}

template <typename T>
bool operator< (std::nullptr_t, copy_ptr<T> const&rhs) {
  typedef typename copy_ptr<T>::pointer V;
  return std::less<V>(nullptr, rhs.get());
}

template <typename T>
bool operator> (copy_ptr<T> const&lhs, std::nullptr_t) {
  return nullptr < lhs;
}

template <typename T>
bool operator> (std::nullptr_t, copy_ptr<T> const&rhs) {
  return rhs < nullptr;
}

template <typename T>
bool operator<=(copy_ptr<T> const&lhs, std::nullptr_t) {
  return !(nullptr < lhs);
}

template <typename T>
bool operator<=(std::nullptr_t, copy_ptr<T> const&rhs) {
  return !(rhs < nullptr);
}

template <typename T>
bool operator>=(copy_ptr<T> const&lhs, std::nullptr_t) {
  return !(lhs < nullptr);
}

template <typename T>
bool operator>=(std::nullptr_t, copy_ptr<T> const&rhs) {
  return !(nullptr < rhs);
}