std::ranges::views::take, std::ranges::take_view

template< ranges::view V >
class take_view
    : public ranges::view_interface<take_view<V>>

namespace views {
    inline constexpr /* unspecified */ take = /* unspecified */;
}

template< ranges::viewable_range R >
    requires /* see below */
constexpr ranges::view auto
    take( R&& r, ranges::range_difference_t<R> count );

template< class DifferenceType >
constexpr /* range adaptor closure */ take( DifferenceType&& count );

views::take(e, f) is expression-equivalent to (where T is std::remove_cvref_t<decltype((e))> and D is ranges::range_difference_t<decltype((e))>):

• ((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the evaluations of e and f are indeterminately sequenced;
• U(ranges::begin(e), ranges::begin(e) + std::min<D>(ranges::distance(e), f)), if T is a specialization of std::span, std::basic_string_view, or ranges::subrange that models both random_access_range and sized_range, where U is
• std::span<typename T::element_type>, if T is a specialization of std::span;
• T, if T is a specialization of std::basic_string_view;
• ranges::subrange<ranges::iterator_t<T>>, if T is a specialization of ranges::subrange;
• ranges::iota_view(*ranges::begin(e),*(ranges::begin(e) + std::min<D>(ranges::distance(e), f))), if T is a specialization of ranges::iota_view that models both random_access_range and sized_range;

• otherwise, take_view(e, f).

take_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, input_range, and sized_range when the underlying view V models respective concepts. It models common_range when the underlying view V models both random_access_range and sized_range.

Data members

Member functions

Deduction guides

Nested classes

Helper templates

template< class T >
constexpr bool enable_borrowed_range<std::ranges::take_view<T>> =
    ranges::enable_borrowed_range<T>;

This specialization of ranges::enable_borrowed_range makes take_view satisfy borrowed_range when the underlying view satisfies it.

Example

#include <algorithm>
#include <iostream>
#include <ranges>

int main()
{
    namespace views = std::views;
    auto print = [](char x){ std::cout << x; };

    for (const char nums[]{'1', '2', '3'};
         int n : views::iota(0, 5))
    {
        std::cout << "take(" << n << "): ";
        // safely takes only upto min(n, nums.size()) elements:
        std::ranges::for_each(nums | views::take(n), print);
        std::cout << '\n';
    }
}

take(0): 
take(1): 1
take(2): 12
take(3): 123
take(4): 123

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also