Example of how to get to the iterator of the vector in a class

fast_for_loop.cc

// Gist https://gist.github.com/mshafae/89f713310ded44cb69295e94c271b7fa
// Filename fast_for_loop.cc
// CompileCommand clang++ -std=c++20 fast_for_loop.cc
// Example of how to get to the iterator of the vector in a class

#include <iostream>
#include <iterator>
#include <vector>

class Wrapper {
public:
  std::vector<int>::const_iterator begin() const { return n.begin();}
  std::vector<int>::const_iterator end() const { return n.end(); }

private:
  std::vector<int> n{10, 11, 12, 13, 14, 15};
};

// From https://www.digitalocean.com/community/tutorials/foreach-loop-c-plus-plus
class NumberRange {
 private:
  int startv;
  int endv;

  // Iterator implementation
  class Iterator {
   private:
    int current;

   public:
    Iterator(int value) : current(value) {}

    int operator*() const { return current; }
    Iterator& operator++() {
      ++current;
      return *this;
    }
    bool operator!=(const Iterator& other) const {
      return current != other.current;
    }
  };

 public:
  NumberRange(int start, int end) : startv(start), endv(end) {}

  Iterator begin() const { return Iterator(startv); }
  Iterator end() const { return Iterator(endv); }
};

int main(int argc, char const* argv[]) {
  for (int i : NumberRange(1, 6)) {
    std::cout << i << " ";  // Outputs: 1 2 3 4 5
  }

  Wrapper p;
  for (const auto& x : p) {
    std::cout << x << "\n";
  }
  return 0;
}