copyableoptional.hh

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// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// SPDX-FileCopyrightInfo: Copyright © DUNE Project contributors, see file LICENSE.md in module root
// SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
#ifndef DUNE_COMMON_COPYABLE_OPTIONAL_HH
#define DUNE_COMMON_COPYABLE_OPTIONAL_HH
 
#include <cassert>
#include <iostream>
#include <memory>
#include <optional>
#include <type_traits>
 
#include <dune/common/typeutilities.hh>
 
namespace Dune {
 
template <class Type>
class CopyableOptional
    : public std::optional<Type>
{
  static_assert(std::is_copy_constructible_v<Type>);
  static_assert(std::is_object_v<Type>);
 
  using Base = std::optional<Type>;
 
public:
 
  template <class T = Type,
    std::enable_if_t<std::is_default_constructible_v<T>, int> = 0>
  constexpr CopyableOptional ()
        noexcept(std::is_nothrow_default_constructible_v<T>)
    : Base{std::in_place}
  {}
 
  template <class T = Type,
    disableCopyMove<CopyableOptional,T> = 0,
    std::enable_if_t<std::is_constructible_v<Type,T&&>, int> = 0,
    std::enable_if_t<std::is_convertible_v<T&&,Type>, int> = 0>
  constexpr CopyableOptional (T&& value)
        noexcept(std::is_nothrow_constructible_v<Type,T&&>)
    : Base{std::in_place, std::forward<T>(value)}
  {}
 
  template <class T = Type,
    disableCopyMove<CopyableOptional,T> = 0,
    std::enable_if_t<std::is_constructible_v<Type,T&&>, int> = 0,
    std::enable_if_t<not std::is_convertible_v<T&&,Type>, int> = 0>
  explicit constexpr CopyableOptional (T&& value)
        noexcept(std::is_nothrow_constructible_v<Type,T&&>)
    : Base{std::in_place, std::forward<T>(value)}
  {}
 
  template <class... Args,
    disableCopyMove<CopyableOptional, Args...> = 0,
    std::enable_if_t<(sizeof...(Args) > 1), int> = 0,
    std::enable_if_t<std::is_constructible_v<Type,Args&&...>, int> = 0>
  constexpr CopyableOptional (Args&&... args)
        noexcept(std::is_nothrow_constructible_v<Type,Args&&...>)
    : Base{std::in_place, std::forward<Args>(args)...}
  {}
 
  constexpr CopyableOptional (const CopyableOptional&) = default;
 
  constexpr CopyableOptional (CopyableOptional&&) = default;
 
  ~CopyableOptional () = default;
 
  constexpr CopyableOptional& operator= (const CopyableOptional& that)
        noexcept(std::is_nothrow_copy_assignable_v<Type> ||
          (!std::is_copy_assignable_v<Type> && std::is_nothrow_copy_constructible_v<Type>))
  {
    if constexpr(std::is_copy_assignable_v<Type>)
      Base::operator=(that);
    else {
      // no self-assignment
      if (this != std::addressof(that)) {
        if (that)
          Base::emplace(*that);
        else
          Base::reset();
      }
    }
    return *this;
  }
 
  template <class T = Type,
    std::enable_if_t<std::is_move_constructible_v<T>, int> = 0>
  constexpr CopyableOptional& operator= (CopyableOptional&& that)
        noexcept(std::is_nothrow_move_assignable_v<Type> ||
          (!std::is_move_assignable_v<Type> && std::is_nothrow_move_constructible_v<Type>))
  {
    if constexpr(std::is_move_assignable_v<Type>)
      Base::operator=(std::move(that));
    else {
      // no self-assignment
      if (this != std::addressof(that)) {
        if (that)
          Base::emplace(std::move(*that));
        else
          Base::reset();
      }
    }
    return *this;
  }
 
  template <class T = Type,
    std::enable_if_t<not std::is_same_v<std::decay_t<T>, CopyableOptional>, int> = 0,
    std::enable_if_t<(std::is_assignable_v<Type&,T> || std::is_constructible_v<Type,T>), int> = 0>
  constexpr CopyableOptional& operator= (T&& value)
        noexcept(std::is_nothrow_assignable_v<Type&,T> ||
          (!std::is_assignable_v<Type&,T> && std::is_nothrow_constructible_v<Type,T>))
  {
    if constexpr(std::is_assignable_v<Type&,T>)
      Base::operator=(std::forward<T>(value));
    else
      Base::emplace(std::forward<T>(value));
    return *this;
  }
};
 
} // end namespace Dune
 
#endif // DUNE_COMMON_COPYABLE_OPTIONAL_HH