std::expected<T,E>::value_or - cppreference.com (original) (raw)
| Primary template | ||
|---|---|---|
| template< class U = std::remove_cv_t<T> > constexpr T value_or( U&& default_value ) const&; | (1) | (since C++23) |
| template< class U = std::remove_cv_t<T> > constexpr T value_or( U&& default_value ) &&; | (2) | (since C++23) |
Returns the expected value if it exists, otherwise returns default_value.
The void partial specialization does not have these member functions.
[edit] Parameters
| default_value | - | the value to use in case *this does not contain an expected value |
|---|
[edit] Return value
has_value() ? **this : static_cast<T>(std::forward<U>(default_value))
has_value() ? std::move(**this) : static_cast<T>(std::forward<U>(default_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 3886 | C++23 | U does not have a default template argument | specified |
[edit] See also
| | returns the expected value (public member function) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns the unexpected value if present, another value otherwise (public member function) [edit] |