22 General utilities library [utilities]

22.5 Optional objects [optional]

22.5.3 Class template optional [optional.optional]

22.5.3.6 Observers [optional.observe]

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