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Showing content from https://timsong-cpp.github.io/cppwp/n4659/optional.observe below:

[optional.observe]

23 General utilities library [utilities] 23.6 Optional objects [optional] 23.6.3 Class template optional [optional.optional] 23.6.3.5 Observers [optional.observe]

constexpr const T* operator->() const; constexpr T* operator->();

Requires: *this contains a value.

Remarks: These functions shall be constexpr functions.

constexpr const T& operator*() const&; constexpr T& operator*() &;

Requires: *this contains a value.

Remarks: These functions shall be constexpr functions.

constexpr T&& operator*() &&; constexpr const T&& operator*() const&&;

Requires: *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 shall be a constexpr function.

constexpr bool has_value() const noexcept;

Returns: true if and only if *this contains a value.

Remarks: This function shall be a constexpr function.

constexpr const T& value() const&; constexpr T& value() &;

Effects: Equivalent to:

return bool(*this) ? *val : throw bad_optional_access();

constexpr T&& value() &&; constexpr const T&& value() const&&;

Effects: Equivalent to:

return bool(*this) ? std::move(*val) : throw bad_optional_access();

template <class U> constexpr T value_or(U&& v) const&;

Effects: Equivalent to:

return bool(*this) ? **this : static_cast<T>(std::forward<U>(v));

Remarks: If is_­copy_­constructible_­v<T> && is_­convertible_­v<U&&, T> is false, the program is ill-formed.

template <class U> constexpr T value_or(U&& v) &&;

Effects: Equivalent to:

return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(v));

Remarks: If is_­move_­constructible_­v<T> && is_­convertible_­v<U&&, T> is false, the program is ill-formed.


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