22 General utilities library [utilities]

22.5 Optional objects [optional]

22.5.3 Class template optional [optional.optional]

22.5.3.7 Observers [optional.observe]

constexpr const T* operator->() const noexcept; constexpr T* operator->() noexcept;
Preconditions: *this contains a value.
Returns: val.
Remarks: These functions are constexpr functions.
constexpr const T& operator*() const & noexcept; constexpr T& operator*() & noexcept;
Preconditions: *this contains a value.
Returns: *val.
Remarks: These functions are constexpr functions.
constexpr T&& operator*() && noexcept; constexpr const T&& operator*() const && noexcept;
Preconditions: *this contains a value.
Effects: Equivalent to: return std​::​move(*val);
constexpr explicit operator bool() const noexcept;
Returns: true if and only if *this contains a value.
Remarks: This function is a constexpr function.
constexpr bool has_value() const noexcept;
Returns: true if and only if *this contains a value.
Remarks: This function is a constexpr function.
constexpr const T& value() const &; constexpr T& value() &;
Effects: Equivalent to: return has_value() ? *val : throw bad_optional_access();
constexpr T&& value() &&; constexpr const T&& value() const &&;
Effects: Equivalent to: return has_value() ? std::move(*val) : throw bad_optional_access();
template<class U> constexpr T value_or(U&& v) const &;
Mandates: is_copy_constructible_v<T> && is_convertible_v<U&&, T> is true.
Effects: Equivalent to: return has_value() ? **this : static_cast<T>(std::forward<U>(v));
template<class U> constexpr T value_or(U&& v) &&;
Mandates: is_move_constructible_v<T> && is_convertible_v<U&&, T> is true.
Effects: Equivalent to: return has_value() ? std::move(**this) : static_cast<T>(std::forward<U>(v));