constexpr decltype(auto) back()
    requires ranges::bidirectional_range<D> && ranges::common_range<D>;
(1) (since C++20)
constexpr decltype(auto) back() const
    requires ranges::bidirectional_range<const D> && ranges::common_range<const D>;
(2) (since C++20)

The default implementation of back() member function returns the last element in the view of the derived type. Whether the element is returned by value or by reference depends on the operator* of the iterator type.

1) Let derived be static_cast<D&>(*this). Equivalent to return *ranges::prev(ranges::end(derived));. The behavior is undefined if empty() is true (i.e. the beginning iterator compares equal to the sentinel), even if the iterator obtained in the same way is dereferenceable.
2) Same as (1), except that derived is static_cast<const D&>(*this).



Return value

The last element in the view.


In C++20, no type derived from std::ranges::view_interface in the standard library provides their own back() member function.

However, following derived types cannot use the default implementations, as they never satisfy neither bidirectional_range nor common_range:

The inherited back() member function is available for std::ranges::empty_view, but a call to it always results in undefined behavior.


See also

returns a reverse iterator to the beginning of a container or array
(function template)
returns a reverse iterator to a range
(customization point object)
returns a reverse iterator to a read-only range
(customization point object)

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