Creating std::ranges::subrange from Multiple Containers

std::ranges::subrange itself cannot directly view data from multiple containers simultaneously since it represents a contiguous range of elements from a single container. However, you can achieve similar functionality using various techniques in C++.

Using Range Proxies

If you need to work with multiple containers, you can create a custom range proxy that iterates over multiple containers. Here’s how you can achieve this with a simple example:

1#include <iostream>
2#include <iterator>
3#include <ranges>
4#include <vector>
5
Multiple Container Iterator|Show
6class MultiContainerIterator {/*...*/};
47
48template <typename Container1, typename Container2>
49class MultiContainerView {
50 public:
51  MultiContainerView(Container1& c1,
52    Container2& c2) : c1_(c1), c2_(c2) {}
53
54  auto begin() {
55    return MultiContainerIterator(c1_.begin(),
56      c1_.end(), c2_.begin());
57  }
58
59  auto end() {
60    return MultiContainerIterator(
61      c1_.end(), c1_.end(), c2_.end()
62    );
63  }
64
65 private:
66  Container1& c1_;
67  Container2& c2_;
68};
69
70int main() {
71  std::vector<int> vec1{1, 2, 3};
72  std::vector<int> vec2{4, 5, 6};
73
74  MultiContainerView view(vec1, vec2);
75
76  for (
77    auto it = view.begin();
78    it != view.end();
79    ++it
80  ) {
81    std::cout << *it << ", ";
82  }
83}

11, 2, 3, 4, 5, 6,

Using std::ranges::views::join

Another way to work with multiple containers is to use std::ranges::views::join to create a single view from multiple ranges. This technique can be useful when you want to treat elements from multiple containers as a single range.

1#include <iostream>
2#include <ranges>
3#include <vector>
4
5int main() {
6  std::vector<std::vector<int>> nested_vec{
7    {1, 2, 3}, {4, 5, 6}};
8
9  auto joined_view = std::views::join(nested_vec);
10
11  for (int n : joined_view) {
12    std::cout << n << ", ";
13  }
14}

11, 2, 3, 4, 5, 6,

Combining Views with zip

Using std::ranges::views::zip, you can combine multiple ranges and iterate over them together, processing elements pairwise or in tuples. For example:

1#include <iostream>
2#include <vector>
3#include <ranges>
4#include <tuple>
5
6int main() {
7  std::vector<int> vec1{1, 2, 3};
8  std::vector<int> vec2{4, 5, 6};
9
10  auto zip_view = std::views::zip(vec1, vec2);
11
12  for (const auto& [a, b] : zip_view) {
13    std::cout << "(" << a << ", " << b << "), ";
14  }
15}

1(1, 4), (2, 5), (3, 6),

Summary

• std::ranges::subrange is designed for single-container ranges.
• Use std::ranges::views::join to concatenate multiple ranges.
• Implement custom range adapters for more control.
• Use std::ranges::views::zip to combine elements from multiple containers.

By employing these techniques, you can effectively manage and iterate over data from multiple containers in a cohesive manner.