boost::counting_iterator range-v3 中的模拟

Question

我想知道是否 range-v3 library has any view/utility providing the functionality similar to boost::counting_iterators?

我一直在寻找那种东西，但似乎没有现成的东西。但是文档不完整（至少 README 是这样建议的）所以也许我忽略了一些东西。

UPD：我实际上要寻找的不仅仅是像 view::iota 这样的整数范围，而是接受任何增量的范围视图（包装器）。一个这样的例子是 Boost.CountingIterator 文档中的以下代码：

int N = 7;
std::vector<int> numbers;
...
// the code below does what I am actually looking for
// I would like to use a single range instead of two separate iterators here
std::vector<std::vector<int>::iterator> pointers;
std::copy(boost::make_counting_iterator(numbers.begin()),
          boost::make_counting_iterator(numbers.end()),
          std::back_inserter(pointers));

Answer 1

我相信 view::ints 就是您要找的。您可以创建一个无限范围，并用 view::take:

之类的内容截断它

using namespace ranges;
int x = accumulate(view::ints(0) | view::take(10), 0); // 45

或者你可以做一个有界的范围（下限包含，上限不包含）

int x = accumulate(view::ints(0, 10), 0);

对于您的示例，您可以改用 view::iota。

copy(view::iota(numbers.begin(), numbers.end()), back_inserter(pointers));

Answer 2

你确实想要 view::iota。它接受任何 WeaklyIncrementable 类型作为范围迭代器类型（不仅是整数类型），以及任何 WeaklyEqualityComparable 到该类型的类型作为范围标记。所以view::iota(0, 8)是整数的范围{0,1,2,3,4,5,6,7}，view::iota(i, s)是迭代器的范围{i,i+1,i+2,...,s}。 boost counting_iterator 示例转换为 range-v3 为 (DEMO):

int N = 7;
std::vector<int> numbers = ranges::view::iota(0, N);

std::vector<std::vector<int>::iterator> pointers =
    ranges::view::iota(numbers.begin(), numbers.end());

std::cout << "indirectly printing out the numbers from 0 to " << N << '\n';
ranges::copy(ranges::view::indirect(pointers),
    ranges::ostream_iterator<>(std::cout, " "));
std::cout << '\n';

boost::counting_iterator range-v3 中的模拟

boost::counting_iterator analogue in range-v3

c++

boost

range-v3