C++
string_view
https://yangacer.blogspot.com/2016/07/c17-stringview.html

#include 

using namespace std;

struct tokenizer {
  tokenizer(string const &s) : m_s(s), m_beg(0), m_end(0) {}
  
  string operator()() {
    for(;m_end < m_s.size();++m_end) {
      if (m_s[m_end] == ',') {
        auto res = m_s.substr(m_beg, m_end - m_beg); // heap access
        m_beg = ++m_end; 
        return res; // heap access
      }
    }
    if (m_end <= m_s.size())
      return m_s.substr(m_beg, m_end); // heap access
  }
  bool more() const { return m_end < m_s.size(); }
private:
  string const &m_s;
  size_t m_beg, m_end;
};

void gendata(string &data, size_t count) {
  for(size_t i=0; i < count; ++i) {
    data.push_back('a'+ i%26);
    if (i+1 != count)
      data.push_back(',');
  }
}

int main() {
  string data;

  gendata(data, 1<<23);
  tokenizer tokr(data);
  
  while(tokr.more()) {
    cout << tokr() << endl;  
  }

  return 0;
}