STD::EXPERIMENTAL::OPTIONAL(3)

💖 std::experimental::optional< _Tp > 💖

okay bestie, welcome to the Library Functions Manual page for std::experimental::optional< _Tp > — yes that's the manual name, yes it's section 3, yes we're doing this together 🫶

---

✨ NAME ✨

std::experimental::optional< _Tp > — the class template for optional values. that's it. that's the whole name. iconic. 💅

---

🌸 SYNOPSIS 🌸

#include <optional>

🎀 Public Types 🎀

• using value_type — yep, that's the one public type. short and sweet, she said what she said 💖

🦋 Public Member Functions 🦋

okay so here's the FULL roster, no skipping, no summarizing, every single overload is getting its moment. the enable_if_t< __and_< ... > > situations are giving very much "i contain multitudes" and we respect it 😭

• construct from _Up &&__t, not convertible — the sneaky non-converting one:

template<typename _Up = _Tp, enable_if_t< __and_< __not_< is_same< optional< _Tp >, decay_t< _Up > > >, is_constructible< _Tp, _Up && >, __not_< is_convertible< _Up &&, _Tp > > >::value, bool > = false> constexpr optional (_Up &&__t)

• construct from _Up &&__t, convertible — same energy but this time it's is_convertible and the bool defaults to true:

template<typename _Up = _Tp, enable_if_t< __and_< __not_< is_same< optional< _Tp >, decay_t< _Up > > >, is_constructible< _Tp, _Up && >, is_convertible< _Up &&, _Tp > >::value, bool > = true> constexpr optional (_Up &&__t)

• construct from const optional< _Up > &__t, not convertible — copy-adjacent, gated on __converts_from_optional being not a thing:

template<typename _Up, enable_if_t< __and_< __not_< is_same< _Tp, _Up > >, is_constructible< _Tp, const _Up & >, __not_< is_convertible< const _Up &, _Tp > >, __not_< __converts_from_optional< _Tp, _Up > > >::value, bool > = false> constexpr optional (const optional< _Up > &__t)

• construct from const optional< _Up > &__t, convertible — the true twin, still refusing __converts_from_optional:

template<typename _Up, enable_if_t< __and_< __not_< is_same< _Tp, _Up > >, is_constructible< _Tp, const _Up & >, is_convertible< const _Up &, _Tp >, __not_< __converts_from_optional< _Tp, _Up > > >::value, bool > = true> constexpr optional (const optional< _Up > &__t)

• move-construct from optional< _Up > &&__t, not convertible — rvalue ref era, bool = false, still no __converts_from_optional:

template<typename _Up, enable_if_t< __and_< __not_< is_same< _Tp, _Up > >, is_constructible< _Tp, _Up && >, __not_< is_convertible< _Up &&, _Tp > >, __not_< __converts_from_optional< _Tp, _Up > > >::value, bool > = false> constexpr optional (optional< _Up > &&__t)

• move-construct from optional< _Up > &&__t, convertible — bool = true, and yes, __converts_from_optional is still blocked:

template<typename _Up, enable_if_t< __and_< __not_< is_same< _Tp, _Up > >, is_constructible< _Tp, _Up && >, is_convertible< _Up &&, _Tp >, __not_< __converts_from_optional< _Tp, _Up > > >::value, bool > = true> constexpr optional (optional< _Up > &&__t)

• emplace (variadic) — the "build it right here from a pile of args" one:

template<typename... _Args> enable_if_t< is_constructible< _Tp, _Args &&... >::value > emplace (_Args &&... __args)

• emplace (initializer_list flavour) — same, but it takes an initializer_list< _Up > first:

template<typename _Up, typename... _Args> enable_if_t< is_constructible< _Tp, initializer_list< _Up > &, _Args &&... >::value > emplace (initializer_list< _Up > __il, _Args &&... __args)

• constexpr operator bool () const noexcept — the boolean-conversion situation, marked noexcept like the confident queen she is.
• constexpr _Tp & operator* () & — deref, lvalue ref flavour.
• constexpr _Tp && operator* () && — deref, rvalue ref flavour.
• constexpr const _Tp & operator* () const & — deref, const lvalue ref flavour.
• constexpr const _Tp && operator* () const && — deref, const rvalue ref flavour. all four ref qualifiers, no crumbs. 👑
• _Tp * operator-> () — the arrow, non-const.
• constexpr const _Tp * operator-> () const — the arrow, const.
• assign from _Up &&__u — note the extra __not_< __and_< is_scalar< _Tp >, is_same< _Tp, decay_t< _Up > > > > gate, very specific, very demure:

template<typename _Up = _Tp> enable_if_t< __and_< __not_< is_same< optional< _Tp >, decay_t< _Up > > >, is_constructible< _Tp, _Up >, __not_< __and_< is_scalar< _Tp >, is_same< _Tp, decay_t< _Up > > > >, is_assignable< _Tp &, _Up > >::value, optional & > operator= (_Up &&__u)

• assign from const optional< _Up > &__u — blocks both __converts_from_optional AND __assigns_from_optional, she has boundaries:

template<typename _Up> enable_if_t< __and_< __not_< is_same< _Tp, _Up > >, is_constructible< _Tp, const _Up & >, is_assignable< _Tp &, _Up >, __not_< __converts_from_optional< _Tp, _Up > >, __not_< __assigns_from_optional< _Tp, _Up > > >::value, optional & > operator= (const optional< _Up > &__u)

• optional & operator= (nullopt_t) noexcept — the nullopt_t assignment, noexcept, no notes.
• assign from optional< _Up > &&__u — rvalue version of that same gated assignment, same two __not_ guards:

template<typename _Up> enable_if_t< __and_< __not_< is_same< _Tp, _Up > >, is_constructible< _Tp, _Up >, is_assignable< _Tp &, _Up >, __not_< __converts_from_optional< _Tp, _Up > >, __not_< __assigns_from_optional< _Tp, _Up > > >::value, optional & > operator= (optional< _Up > &&__u)

• swap — swaps with __other, and its noexcept-ness is exactly whatever this says it is, nothing more:

void swap (optional &__other) noexcept(is_nothrow_move_constructible< _Tp >() &&__is_nothrow_swappable< _Tp >::value)

• constexpr _Tp & value () & — value getter, lvalue ref flavour.
• constexpr _Tp && value () && — value getter, rvalue ref flavour.
• constexpr const _Tp & value () const & — value getter, const lvalue ref flavour.
• constexpr const _Tp && value () const && — value getter, const rvalue ref flavour. again, all four, because consistency is a love language. ✨
• template<typename _Up> _Tp value_or (_Up &&__u) && — the value_or fallback, rvalue flavour.
• template<typename _Up> constexpr _Tp value_or (_Up &&__u) const & — the value_or fallback, const lvalue flavour, this one's constexpr.

---

💜 Detailed Description 💜

template<typename _Tp>
class std::experimental::optional< _Tp >

"Class template for optional values."

that's the whole description bestie, short, sweet, and honestly kind of mysterious of her. the quote marks are load-bearing, i don't make the rules. 🌸

---

🌈 Author 🌈

Generated automatically by Doxygen for libstdc++ from the source code. not a human, not a committee, just Doxygen doing its little thing and we thank it for its service 🫶

---

okay that's the whole page, every overload accounted for, nobody left behind 💖 this one lives in the libstdc++ manual, section 3, and the whole thing was auto-generated from the source code — so when you cite it, cite libstdc++, std::experimental::optional< _Tp >, section 3. mwah. 😘💅