std::optional<T>::and_then

 

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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)

Deduction guides

Helper classes

hash (C++17)

nullopt_t (C++17)

in_place_t (C++17)

bad_optional_access (C++17)

Helper objects

nullopt (C++17)

in_place (C++17)

 

template< class F > constexpr auto and_then( F&& f ) &;	(1)	(since C++23)
template< class F > constexpr auto and_then( F&& f ) const&;	(2)	(since C++23)
template< class F > constexpr auto and_then( F&& f ) &&;	(3)	(since C++23)
template< class F > constexpr auto and_then( F&& f ) const&&;	(4)	(since C++23)

Returns the result of invocation of f on the contained value if it exists. Otherwise, returns an empty value of the return type.

The return type (see below) must be a specialization of std::optional. Otherwise, the program is ill-formed.

1) Equivalent to
if (*this)

    return std::invoke(std::forward<F>(f), this->value());
else

    return std::remove_cvref_t<std::invoke_result_t<F, T&>>();.

2) Equivalent to
if (*this)

    return std::invoke(std::forward<F>(f), this->value());
else

    return std::remove_cvref_t<std::invoke_result_t<F, const T&>>();.

3) Equivalent to
if (*this)

    return std::invoke(std::forward<F>(f), std::move(this->value()));
else

    return std::remove_cvref_t<std::invoke_result_t<F, T>>();.

4) Equivalent to
if (*this)

    return std::invoke(std::forward<F>(f), std::move(this->value()));
else

    return std::remove_cvref_t<std::invoke_result_t<F, const T>>();.

Parameters

f

-

a suitable function or Callable object that returns an std::optional

Return value

The result of f or an empty std::optional, as described above.

Notes

Some languages call this operation flatmap.

Feature testing macro: __cpp_lib_monadic_optional

See also

value_or	returns the contained value if available, another value 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)
or_else (C++23)	returns the optional itself if it contains a value, or the result of the given function otherwise (public member function)