NAME

       std::optional< _Tp > - Class template for optional values.

SYNOPSIS

       Inherits std::_Optional_base< _Tp, bool, bool >, and _Enable_copy_move<
       is_copy_constructible_v< _Tp >, __and_v< is_copy_constructible< _Tp >, is_copy_assignable<
       _Tp > >, is_move_constructible_v< _Tp >, __and_v< is_move_constructible< _Tp >,
       is_move_assignable< _Tp > >, optional< _Tp > >.

   Public Types
       using value_type = _Tp

   Public Member Functions
       template<typename _Up  = _Tp, _Requires< __not_self< _Up >, __not_tag< _Up >,
           is_constructible< _Tp, _Up >, is_convertible< _Up, _Tp >>  = true> constexpr optional
           (_Up &&__t) noexcept(is_nothrow_constructible_v< _Tp, _Up >)
       template<typename _Up  = _Tp, _Requires< __not_self< _Up >, __not_tag< _Up >,
           is_constructible< _Tp, _Up >, __not_< is_convertible< _Up, _Tp >>>  = false> constexpr
           optional (_Up &&__t) noexcept(is_nothrow_constructible_v< _Tp, _Up >)
       template<typename _Up , _Requires< __not_< is_same< _Tp, _Up >>, is_constructible< _Tp,
           const _Up & >, is_convertible< const _Up &, _Tp >, __not_< __converts_from_optional<
           _Tp, _Up >>>  = true> constexpr optional (const optional< _Up > &__t)
           noexcept(is_nothrow_constructible_v< _Tp, const _Up & >)
       template<typename _Up , _Requires< __not_< is_same< _Tp, _Up >>, is_constructible< _Tp,
           const _Up & >, __not_< is_convertible< const _Up &, _Tp >>, __not_<
           __converts_from_optional< _Tp, _Up >>>  = false> constexpr optional (const optional<
           _Up > &__t) noexcept(is_nothrow_constructible_v< _Tp, const _Up & >)
       template<typename... _Args, _Requires< is_constructible< _Tp, _Args... >>  = false>
           constexpr optional (in_place_t, _Args &&... __args)
           noexcept(is_nothrow_constructible_v< _Tp, _Args... >)
       template<typename _Up , typename... _Args, _Requires< is_constructible< _Tp,
           initializer_list< _Up > &, _Args... >>  = false> constexpr optional (in_place_t,
           initializer_list< _Up > __il, _Args &&... __args) noexcept(is_nothrow_constructible_v<
           _Tp, initializer_list< _Up > &, _Args... >)
       constexpr optional (nullopt_t) noexcept
       template<typename _Up , _Requires< __not_< is_same< _Tp, _Up >>, is_constructible< _Tp,
           _Up >, is_convertible< _Up, _Tp >, __not_< __converts_from_optional< _Tp, _Up >>>  =
           true> constexpr optional (optional< _Up > &&__t) noexcept(is_nothrow_constructible_v<
           _Tp, _Up >)
       template<typename _Up , _Requires< __not_< is_same< _Tp, _Up >>, is_constructible< _Tp,
           _Up >, __not_< is_convertible< _Up, _Tp >>, __not_< __converts_from_optional< _Tp, _Up
           >>>  = false> constexpr optional (optional< _Up > &&__t)
           noexcept(is_nothrow_constructible_v< _Tp, _Up >)
       template<typename... _Args> constexpr enable_if_t< is_constructible_v< _Tp, _Args... >,
           _Tp & > emplace (_Args &&... __args) noexcept(is_nothrow_constructible_v< _Tp,
           _Args... >)
       template<typename _Up , typename... _Args> constexpr enable_if_t< is_constructible_v< _Tp,
           initializer_list< _Up > &, _Args... >, _Tp & > emplace (initializer_list< _Up > __il,
           _Args &&... __args) noexcept(is_nothrow_constructible_v< _Tp, initializer_list< _Up >
           &, _Args... >)
       constexpr bool has_value () const noexcept
       constexpr operator bool () const noexcept
       constexpr _Tp && operator* () &&noexcept
       constexpr _Tp & operator* () &noexcept
       constexpr const _Tp && operator* () const &&noexcept
       constexpr const _Tp & operator* () const &noexcept
       constexpr const _Tp * operator-> () const noexcept
       constexpr _Tp * operator-> () noexcept
       template<typename _Up  = _Tp> constexpr enable_if_t< __and_v< __not_self< _Up >, __not_<
           __and_< is_scalar< _Tp >, is_same< _Tp, decay_t< _Up > > > >, is_constructible< _Tp,
           _Up >, is_assignable< _Tp &, _Up > >, optional & > operator= (_Up &&__u)
           noexcept(__and_v< is_nothrow_constructible< _Tp, _Up >, is_nothrow_assignable< _Tp &,
           _Up >>)
       template<typename _Up > constexpr enable_if_t< __and_v< __not_< is_same< _Tp, _Up > >,
           is_constructible< _Tp, const _Up & >, is_assignable< _Tp &, const _Up & >, __not_<
           __converts_from_optional< _Tp, _Up > >, __not_< __assigns_from_optional< _Tp, _Up > >
           >, optional & > operator= (const optional< _Up > &__u) noexcept(__and_v<
           is_nothrow_constructible< _Tp, const _Up & >, is_nothrow_assignable< _Tp &, const _Up
           & >>)
       constexpr optional & operator= (nullopt_t) noexcept
       template<typename _Up > constexpr enable_if_t< __and_v< __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 > >
           >, optional & > operator= (optional< _Up > &&__u) noexcept(__and_v<
           is_nothrow_constructible< _Tp, _Up >, is_nothrow_assignable< _Tp &, _Up >>)
       constexpr void reset () noexcept
       constexpr void swap (optional &__other) noexcept(is_nothrow_move_constructible_v< _Tp >
           &&is_nothrow_swappable_v< _Tp >)
       constexpr _Tp & value () &
       constexpr _Tp && value () &&
       constexpr const _Tp & value () const &
       constexpr const _Tp && value () const &&
       template<typename _Up > constexpr _Tp value_or (_Up &&__u) &&
       template<typename _Up > constexpr _Tp value_or (_Up &&__u) const &

Detailed Description

   template<typename _Tp>
       class std::optional< _Tp >" Class template for optional values.

       Definition at line 662 of file optional.

Author

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