std::expected<T,E>::value
From cppreference.com
| 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.
Return value
1,2)
val3,4) std::move(
val)Exceptions
1,2,5) Throws std::bad_expected_access(std::as_const(error())) if *this contains an unexpected value.
Example
| This section is incomplete Reason: no example |
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 |
See also
| returns the expected value if present, another value otherwise (public member function) | |
| accesses the expected value (public member function) | |
| returns the unexpected value (public member function) | |
| (C++23) |
exception indicating checked access to an expected that contains an unexpected value (class template) |