A lazy pipeline with std::generator

A coroutine returning std::generator produces values on demand: nothing runs until the caller iterates, and nothing is stored.

#include <generator>
#include <iostream>

// Lazy: nothing runs until the caller iterates.
std::generator<int> evens(int upto) {
    for (int i = 0; i < upto; i += 2) co_yield i;
}

int main() {
    for (int v : evens(10)) std::cout << v << ' ';
    std::cout << '\n';
}

Observed output:

0 2 4 6 8

Facts verified 2026-11-04. The code on this page was compiled and run on the box with GCC 16.2.0 at -std=c++23 -Wall -Wextra; the outputs quoted are the observed outputs. MSVC was not tested.

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