C++: What is std::span and its relationship with iterators?

1#include <span>
2
3std::vector<int> vec = {1, 2, 3, 4, 5};
4std::span<int> s(vec);
5
6// Iterator interface
7auto it = s.begin();
8std::cout << *it;  // 1
9++it;
10std::cout << *it;  // 2
11
12// Range-based for
13for (int& x : s) {
14    x *= 2;
15}
16
17// STL algorithms
18std::sort(s.begin(), s.end());
19auto pos = std::find(s.begin(), s.end(), 3);
20auto count = std::count_if(s.begin(), s.end(),
21    [](int x) { return x > 2; });
22
23// Reverse iterators
24for (auto rit = s.rbegin(); rit != s.rend(); ++rit) {
25    std::cout << *rit << " ";
26}
27
28// As contiguous range
29static_assert(std::ranges::contiguous_range<std::span<int>>);
30static_assert(std::ranges::sized_range<std::span<int>>);
31
32// Data access
33int* data = s.data();
34std::cout << s[0];      // Bounds-checked
35std::cout << s.at(0);   // Throws on out-of-bounds