22 General utilities library [utilities]

22.8 Expected objects [expected]

22.8.7 Partial specialization of expected for void types [expected.void]

22.8.7.6 Observers [expected.void.obs]

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constexpr explicit operator bool() const noexcept; constexpr bool has_value() const noexcept;
1
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Returns: has_val.
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constexpr void operator*() const noexcept;
2
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Preconditions: has_value() is true.
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constexpr void value() const &;
3
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Mandates: is_copy_constructible_v<E> is true.
4
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Throws: bad_expected_access(error()) if has_value() is false.
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constexpr void value() &&;
5
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Mandates: is_copy_constructible_v<E> is true and is_move_constructible_v<E> is true.
6
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Throws: bad_expected_access(std​::​move(error())) if has_value() is false.
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constexpr const E& error() const & noexcept; constexpr E& error() & noexcept;
7
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Preconditions: has_value() is false.
8
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Returns: unex.
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constexpr E&& error() && noexcept; constexpr const E&& error() const && noexcept;
9
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Preconditions: has_value() is false.
10
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Returns: std​::​move(unex).
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template<class G = E> constexpr E error_or(G&& e) const &;
11
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Mandates: is_copy_constructible_v<E> is true and is_convertible_v<G, E> is true.
12
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Returns: std​::​forward<G>(e) if has_value() is true, error() otherwise.
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template<class G = E> constexpr E error_or(G&& e) &&;
13
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Mandates: is_move_constructible_v<E> is true and is_convertible_v<G, E> is true.
14
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Returns: std​::​forward<G>(e) if has_value() is true, std​::​move(error()) otherwise.