cpp-descriptive-pointers/value_ptr.hpp

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

#pragma once

#include <memory>

#include "pointer_fwd.hpp"
#include "ptr_compare.hpp"

namespace detail {
  template <typename T>
  using clone_func = T* (T::*)() const;
  
  template <typename T, typename = void>
  class value_ptr_copy;
  
  template <typename T>
  struct value_ptr_copy<T, typename std::enable_if<!std::is_polymorphic<T>::value>::type> {
    T * Copy( T * ptr ) const { return ptr ? new T(*ptr) : nullptr; }
  };

#define POLYMORPHIC_VALUE_PTR_GROUP_FROM_CLONE_FUNCTION( fclone ) \
  template <typename T> \
  struct value_ptr_copy<T, typename std::enable_if<std::is_polymorphic<T>::value \
      && std::is_same<clone_func<T>, decltype(&T::fclone)>::value>::type> { \
    T * Copy( T * ptr ) const { return ptr ? ptr->fclone() : nullptr; } \
  }

  POLYMORPHIC_VALUE_PTR_GROUP_FROM_CLONE_FUNCTION( Clone );
  POLYMORPHIC_VALUE_PTR_GROUP_FROM_CLONE_FUNCTION( clone );
  POLYMORPHIC_VALUE_PTR_GROUP_FROM_CLONE_FUNCTION( Copy );
  POLYMORPHIC_VALUE_PTR_GROUP_FROM_CLONE_FUNCTION( copy );
}

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

POINTER_TEMPLATE_COMPARE( value_ptr )