STD::_OPTIONAL_BASE(3cxx)

✨ std::_Optional_base< _Tp, bool, bool > ✨

okay bestie, welcome to the 3cxx manual 💖 you're reading the page for std::_Optional_base< _Tp, bool, bool >, and yes the name is a whole mouthful, we love that for it 🫶

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🌸 NAME 🌸

std::_Optional_base< _Tp, bool, bool > — the class template that hands optional its copy/move constructors. that's literally its whole job. main character behavior, honestly 👑

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🎀 SYNOPSIS 🎀

#include <optional>

Inherited by std::experimental::fundamentals_v1::optional< _Tp > [private], and std::optional< _Tp > [private]. so like… two very iconic children, both keeping it private 🔒✨

💅 Public Member Functions

• constexpr _Optional_base (_Optional_base &&__other) noexcept(is_nothrow_move_constructible_v< _Tp >) — move-constructs from another one. no cap, whether it's noexcept depends entirely on whether _Tp is nothrow move constructible.
• constexpr _Optional_base (const _Optional_base &__other) — copies from another one. classic.
• template<typename... _Args, enable_if_t< is_constructible_v< _Tp, _Args... >, bool > = false> constexpr _Optional_base (in_place_t, _Args &&... __args) — the in_place_t one, where you hand it args and it builds the value right there in place. only exists when _Tp is constructible from those _Args..., otherwise SFINAE just quietly deletes it from existence 🙈
• 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) — same energy but with an initializer_list< _Up > __il in the mix. also gated on constructibility, bestie.
• _Optional_base & operator= (_Optional_base &&)=default — move assignment, defaulted. periodt.
• _Optional_base & operator= (const _Optional_base &)=default — copy assignment, defaulted. also periodt.

✨ Public Attributes

• _Optional_payload< _Tp > _M_payload — the actual payload member. the whole vibe lives in here 🍓

🧚 Protected Types

• using _Stored_type — a protected type alias. mysterious. lowkey iconic.

🌈 Protected Member Functions

• template<typename... _Args> constexpr void _M_construct (_Args &&... __args) noexcept(is_nothrow_constructible_v< _Stored_type, _Args... >) — constructs the stored thing-y from __args. its nothrow-ness is inherited from whether _Stored_type is nothrow constructible from those args.
• constexpr void _M_destruct () noexcept — destroys it. no drama, marked noexcept.
• constexpr const _Tp & _M_get () const noexcept — const getter, returns a const _Tp &.
• constexpr _Tp & _M_get () noexcept — non-const getter, returns a _Tp &. yes there are two, we love overloading 💕
• constexpr bool _M_is_engaged () const noexcept — are we engaged or not?? (as in, does it hold a value. not, like, romantically. though 👀)
• constexpr void _M_reset () noexcept — resets everything. goodbye value 💀

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🌟 Detailed Description 🌟

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." yes ma'am 💖

okay so here's the tea ☕ a separate base class template like this is necessary so that the copy/move constructors can be conditionally trivial. it's giving "i have to be my own class to make my constructors behave."

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. and otherwise?? they will invoke _Optional_payload(bool, const _Optional_payload&) or _Optional_payload(bool, _Optional_payload&&) to initialize the contained value — but only if we're copying/moving an engaged optional 🫶

and 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

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💜 Author 💜

Generated automatically by Doxygen for libstdc++ from the source code. not a human bestie, just the machines doing their little machine thing 🤖✨

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⚠️ heads up: this is auto-generated Doxygen output for libstdc++, on the 3cxx manual — that's the vibe, that's the source, no cap.

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okay that's the whole page, you ate it 💅 go forth and understand your _Optional_base the way it deserves, bestie. libstdc++ out here, 3cxx manual, generated by Doxygen, mwah 🎀