std::optional<T>::or_else
template< class F > constexpr optional or_else( F&& f ) const&; |
(1) | (since C++23) |
template< class F > constexpr optional or_else( F&& f ) &&; |
(2) | (since C++23) |
Returns *this
if it contains a value. Otherwise, returns the result of f
.
The program is ill-formed if std::remove_cvref_t<std::invoke_result_t<F>>
is not same as std::optional<T>
.
1) Equivalent to
return *this ? *this : std::forward<F>(f)();
. This overload participates in overload resolution only if both
std::copy_constructible<T>
and
std::invocable<F>
are modeled.
2) Equivalent to
return *this ? std::move(*this) : std::forward<F>(f)();
. This overload participates in overload resolution only if both
std::move_constructible<T>
and
std::invocable<F>
are modeled.
Parameters
f | - | a function or Callable object that returns an std::optional<T> |
Return value
*this
or the result of f
, as described above.
Notes
Feature testing macro: __cpp_lib_monadic_optional
.
Example
See also
returns the contained value if available, another value otherwise (public member function) |
|
(C++23)
|
returns the result of the given function on the contained value if it exists, or an empty optional otherwise (public member function) |
(C++23)
|
returns an optional containing the transformed contained value if it exists, or an empty optional otherwise (public member function) |
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