deletable_object.hpp

//
// Copyright (c) 2018-2020 Manuel Pöter.
// Licensed under the MIT License. See LICENSE file in the project root for full license information.
//
 
#ifndef XENIUM_DETAIL_DELETABLE_OBJECT_HPP
#define XENIUM_DETAIL_DELETABLE_OBJECT_HPP
 
#include <memory>
#include <type_traits>
 
#ifdef _MSC_VER
  #pragma warning(push)
  #pragma warning(disable : 26495) // uninitialized member variable
#endif
 
namespace xenium::reclamation::detail {
 
struct deletable_object {
  virtual void delete_self() = 0;
  deletable_object* next = nullptr;
 
protected:
  virtual ~deletable_object() = default;
};
 
inline void delete_objects(deletable_object*& list) {
  auto* cur = list;
  for (deletable_object* next = nullptr; cur != nullptr; cur = next) {
    next = cur->next;
    cur->delete_self();
  }
  list = nullptr;
}
 
template <class Derived, class DeleterT, class Base>
struct deletable_object_with_non_empty_deleter : Base {
  using Deleter = DeleterT;
  void delete_self() override {
    auto& my_deleter = reinterpret_cast<Deleter&>(_deleter_buffer);
    Deleter deleter(std::move(my_deleter));
    my_deleter.~Deleter(); // NOLINT (use-after-move)
 
    deleter(static_cast<Derived*>(this));
  }
 
  void set_deleter(Deleter deleter) { new (&_deleter_buffer) Deleter(std::move(deleter)); }
 
private:
  using buffer = typename std::aligned_storage<sizeof(Deleter), alignof(Deleter)>::type;
  buffer _deleter_buffer;
};
 
template <class Derived, class DeleterT, class Base>
struct deletable_object_with_empty_deleter : Base {
  using Deleter = DeleterT;
  void delete_self() override {
    static_assert(std::is_default_constructible<Deleter>::value, "empty deleters must be default constructible");
    Deleter deleter{};
    deleter(static_cast<Derived*>(this));
  }
 
  void set_deleter(Deleter /*deleter*/) {}
};
 
template <class Derived, class Deleter = std::default_delete<Derived>, class Base = deletable_object>
using deletable_object_impl = std::conditional_t<std::is_empty<Deleter>::value,
                                                 deletable_object_with_empty_deleter<Derived, Deleter, Base>,
                                                 deletable_object_with_non_empty_deleter<Derived, Deleter, Base>>;
} // namespace xenium::reclamation::detail
 
#ifdef _MSC_VER
  #pragma warning(pop)
#endif
 
#endif