# std::expected<T,E>::value

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< cpp‎ | utility‎ | expected

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()`.

1,2) If std::is_copy_constructible_v <E> is false, the program is ill-formed.
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.
5) If std::is_copy_constructible_v <E> is false, the program is ill-formed.
6) If std::is_move_constructible_v <E> is false, the program is ill-formed.

### Return value

1,2) `val`
3,4) std::move(`val`)

### Exceptions

1,2,5) Throws std::bad_expected_access ( std::as_const (error())) if *this contains an unexpected value.
3,4,6) Throws std::bad_expected_access (std::move(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

value_or | returns the expected value if present, another value otherwise (public member function)
operator->operator* | accesses the expected value (public member function)
error | returns the unexpected value (public member function)
bad_expected_access (C++23) | exception indicating checked access to an `expected` that contains an unexpected value (class template)

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