STD::_OPTIONAL_BASE(3)

📦
version 13.3.1 · 3 versions
, in centos-stream 9

okay so bestie 💖 welcome to the std::_Opti...ol, bool >(3) page — it’s from the Library Functions Manual, and it’s all about a very specific little base class. Buckle up, we’re going in. 🎀

💖 NAME 💖

  • std::_Optional_base< _Tp, bool, bool > — Class template that provides copy/move constructors of optional. That’s the whole name-and-purpose situation, periodt. 💅

✨ SYNOPSIS ✨

okay so first, the inheritance tea ☕:

  • Inherits std::_Optional_base_impl< _Tp, _Dp >.

and it’s inherited by this whole squad:

  • std::optional< _Inner_iter > [private]
  • std::experimental::fundamentals_v1::optional< _Tp > [private]
  • std::optional< _Tp > [private]
  • std::ranges::__detail::__non_propagating_cache< _Tp > [protected]

🌸 Public Member Functions 🌸

  • constexpr _Optional_base (_Optional_base &&__other) noexcept(is_nothrow_move_constructible_v< _Tp >)
  • constexpr _Optional_base (const _Optional_base &__other)
  • template<typename... _Args, enable_if_t< is_constructible_v< _Tp, _Args... >, bool > = false> constexpr _Optional_base (in_place_t, _Args &&... __args)
  • template<typename _Up , typename... _Args, enable_if_t< is_constructible_v< _Tp, initializer_list< _Up > &, _Args... >, bool > = false> constexpr _Optional_base (in_place_t, initializer_list< _Up > __il, _Args &&... __args)
  • _Optional_base & operator= (_Optional_base &&)=default
  • _Optional_base & operator= (const _Optional_base &)=default

🧚 Public Attributes 🧚

  • _Optional_payload< _Tp > _M_payload — the one public attribute, living its best life. 🫶

🦋 Protected Types 🦋

  • using _Stored_type = remove_const_t< _Tp >

💅 Protected Member Functions 💅

  • template<typename... _Args> constexpr void _M_construct (_Args &&... __args) noexcept(is_nothrow_constructible_v< _Stored_type, _Args... >)
  • constexpr void _M_destruct () noexcept
  • constexpr const _Tp & _M_get () const noexcept
  • constexpr _Tp & _M_get () noexcept
  • constexpr bool _M_is_engaged () const noexcept
  • constexpr void _M_reset () noexcept

🌈 Detailed Description 🌈

the template signature is giving:

template<typename _Tp, bool = is_trivially_copy_constructible_v<_Tp>, bool =
       is_trivially_move_constructible_v<_Tp>>
       struct std::_Optional_base< _Tp, bool, bool >" Class template that
       provides copy/move constructors of optional.

and the reason is literally this: Such a separate base class template is necessary in order to conditionally make copy/move constructors trivial. That’s the whole assignment. 💅

When the contained value is trivially copy/move constructible, the copy/move constructors of _Optional_base will invoke the trivial copy/move constructor of _Optional_payload. Otherwise, they will invoke _Optional_payload(bool, const _Optional_payload&) or _Optional_payload(bool, _Optional_payload&&) to initialize the contained value, if copying/moving an engaged optional.

Whether the other special members are trivial is determined by the _Optional_payload<_Tp> specialization used for the _M_payload member. iykyk. 🧚

👀 See also 👀

  • optional
  • _Enable_special_members

🌟 Author 🌟

Generated automatically by Doxygen for libstdc++ from the source code. No human author to hype up, just Doxygen doing its little automated thing. 🤖💖

later bestie 💅 — this page is from libstdc++, dated Fri Feb 14 2025, and the title is std::_Opti...ol, bool >(3). mwah 💋

📦 where this page comes from