std::expected<T,E>::value - cppreference.com (original) (raw)
| 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().
[edit] Return value
3,4) std::move(_val_)
[edit] Exceptions
3,4,6) Throws std::bad_expected_access(std::move(error())) if *this contains an unexpected value.
[edit] 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
| | returns the expected value if present, another value otherwise (public member function) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | accesses the expected value (public member function) [edit] | | | returns the unexpected value (public member function) [edit] | | | exception indicating checked access to an expected that contains an unexpected value (class template) [edit] |