Creating a View of Elements at Even Indices

Creating a view that includes only the elements at even indices can be accomplished using std::views::filter() along with a lambda function. The lambda function will check if the index of each element is even.

First, let's set up our example:

1#include <iostream>
2#include <ranges>
3#include <vector>
4
5int main() {
6  std::vector<int> Numbers{1, 2, 3, 4, 5, 6, 7, 8};
7
8  auto EvenIndexView = Numbers
9    | std::views::filter([i = 0](int) mutable {
10      return i++ % 2 == 0;
11  });
12
13  for (int Num : EvenIndexView) {
14    std::cout << Num << ", ";
15  }
16}

11, 3, 5, 7,

In this example, we use a mutable lambda with a captured index variable i that increments with each call. The lambda returns true only for even indices. The std::views::filter() function uses this lambda to filter the Numbers vector.

Explanation

• The mutable lambda allows modification of the captured variable i on each call.
• i++ % 2 == 0 ensures that only elements with even indices are included.
• The EvenIndexView is created by applying the filter view to the Numbers vector.

This approach efficiently creates a view without needing additional storage, maintaining the non-owning nature of views.