24 Ranges library [ranges]

take_­view produces a view of the first N elements from another view, or all the elements if the adapted view contains fewer than N.

The name views​::​take denotes a range adaptor object ([range.adaptor.object]).

Let E and F be expressions, let T be remove_­cvref_­t<decltype((E))>, and let D be range_­difference_­t<decltype((E))>.

If decltype((F)) does not model convertible_­to<D>, views​::​take(E, F) is ill-formed.

Otherwise, the expression views​::​take(E, F) is expression-equivalent to:

• (2.1)
  If T is a specialization of ranges​::​empty_­view ([range.empty.view]), then ((void) F, decay-copy(E)).
• (2.2)
  Otherwise, if T models random_­access_­range and sized_­range and is

  • (2.2.1)
    a specialization of span ([views.span]) where T​::​extent == dynamic_­extent,
  • (2.2.2)
    a specialization of basic_­string_­view ([string.view]),
  • (2.2.3)
    a specialization of ranges​::​iota_­view ([range.iota.view]), or
  • (2.2.4)
    a specialization of ranges​::​subrange ([range.subrange]),

  then T{ranges​::​begin(E), ranges​::​begin(E) + min<D>(ranges​::​size(E), F)}, except that E is evaluated only once.
• (2.3)
  Otherwise, ranges​::​take_­view{E, F}.