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std::optional<T>::and_then

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< cpp‎ | utility‎ | optional
 
 
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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>>();
.

Contents

[edit] Parameters

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

[edit] Return value

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

[edit] Notes

Some languages call this operation flatmap.

[edit] Example

[edit] See also

returns the contained value if available, another value otherwise
(public member function) [edit]
(C++23)
returns an optional containing the transformed contained value if it exists, or an empty optional otherwise
(public member function) [edit]
(C++23)
returns the optional itself if it contains a value, or the result of the given function otherwise
(public member function) [edit]