24 Ranges library [ranges]

24.5 Range utilities [range.utility]

24.5.2 View interface [view.interface]

24.5.2.1 Members [view.interface.members]

constexpr decltype(auto) front() requires forward_range<D>;
constexpr decltype(auto) front() const requires forward_range<const D>;

Preconditions: !empty().

Effects: Equivalent to: return *ranges::begin(derived());

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constexpr decltype(auto) back() requires bidirectional_range<D> && common_range<D>;
constexpr decltype(auto) back() const
  requires bidirectional_range<const D> && common_range<const D>;

Preconditions: !empty().

Effects: Equivalent to: return *ranges::prev(ranges::end(derived()));