std::optional<T>::or_else

 

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std::optional

Member functions

optional::optional (C++17)

optional::~optional (C++17)

optional::operator= (C++17)

Observers

optional::operator->optional::operator* (C++17)(C++17)

optional::operator booloptional::has_value (C++17)(C++17)

optional::value (C++17)

optional::value_or (C++17)

Monadic operations

optional::and_then (C++23)

optional::transform (C++23)

optional::or_else (C++23)

Modifiers

optional::emplace (C++17)

optional::swap (C++17)

optional::reset (C++17)

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++17)(C++17)(C++17)(C++17)(C++17)(C++17)(C++20)

make_optional (C++17)

swap (C++17)

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hash (C++17)

nullopt_t (C++17)

in_place_t (C++17)

bad_optional_access (C++17)

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nullopt (C++17)

in_place (C++17)

 

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-test macro	Value	Std	Comment
__cpp_lib_optional	202110L	(C++23)	Monadic operations in std::optional

See also

value_or	returns the contained value if available, another value otherwise (public member function)
and_then (C++23)	returns the result of the given function on the contained value if it exists, or an empty optional otherwise (public member function)
transform (C++23)	returns an optional containing the transformed contained value if it exists, or an empty optional otherwise (public member function)