#include <iostream>
#include <coroutine>
#include <ranges>

std::generator<unsigned> gen(unsigned start, unsigned step = 1) {
    while(1) {
        co_yield start += step;
    }
}

int main() {
    auto g = gen(0);
    for(auto i : std::views::iota(0, 100)) {
        std::cout << g << std::endl;
    }
}

root@c7c77c58b545:/usr/src/myapp# c++ -std=c++2a -fcoroutines gen.cpp
gen.cpp:5:6: error: 'generator' in namespace 'std' does not name a template type; did you mean 'generate'?
    5 | std::generator<unsigned> gen(unsigned start, unsigned step = 1) {
      |      ^~~~~~~~~
      |      generate
gen.cpp: In function 'int main()':
gen.cpp:12:14: error: 'gen' was not declared in this scope
   12 |     auto g = gen(0);
      |              ^~~