std::expected<T,E>::value_or
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std::expected
expected::value_or
Primary template
template< class U = std::remove_cv_t <T> >
constexpr T value_or( U&& default_value ) const&;
(1)
(since C++23)
constexpr T value_or( U&& default_value ) const&;
template< class U = std::remove_cv_t <T> >
constexpr T value_or( U&& default_value ) &&;
(2)
(since C++23)
constexpr T value_or( U&& default_value ) &&;
Returns the expected value if it exists, otherwise returns default_value.
The void partial specialization does not have these member functions.
1) If std::is_copy_constructible_v <T> or std::is_convertible_v <U, T> is false, the program is ill-formed.
2) If std::is_move_constructible_v <T> or std::is_convertible_v <U, T> is false, the program is ill-formed.
[edit] Parameters
default_value
-
the value to use in case *this does not contain an expected value
[edit] Return value
1) has_value() ? **this : static_cast<T>(std::forward <U>(default_value))
2) has_value() ? std::move(**this) : static_cast<T>(std::forward <U>(default_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 3886 | C++23 | U does not have a default template argument
|
specified |