std::expected<T,E>::value
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std::expected
expected::value
Primary template
constexpr T& value() &;
(1)
(since C++23)
constexpr const T& value() const&;
(2)
(since C++23)
constexpr T&& value() &&;
(3)
(since C++23)
constexpr const T&& value() const&&;
(4)
(since C++23)
void partial specialization
constexpr void value() const&;
(5)
(since C++23)
constexpr void value() &&;
(6)
(since C++23)
If *this contains an expected value, returns a reference to the contained value. Returns nothing for void partial specialization.
Otherwise, throws an exception of type std::bad_expected_access <std::decay_t <E>> that contains a copy of error().
3,4) If std::is_copy_constructible_v <E> or std::is_constructible_v <E, decltype(std::move(error()))> is false, the program is ill-formed.
[edit] Return value
1,2)
val 3,4) std::move(
val)[edit] Exceptions
1,2,5) Throws std::bad_expected_access (std::as_const (error())) if *this contains an unexpected value.
[edit] Example
This section is incomplete
Reason: no example
Reason: no example
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3940 | C++23 | E was not required to be copy/move-constructible for overloads (5,6)
|
required |
[edit] See also
(C++23)
expected that contains an unexpected value (class template) [edit]