How to run a Lua coroutine in C++ with sol3?

Question

I'm using sol2 (v3.3.0) in C++ to run Lua coroutines. I want to pass a Lua function to C++ and execute it as a coroutine. However, my attempts to convert sol::function to sol::coroutine are not working.

Here is a minimal example that doesn't work:

#include <sol/sol.hpp>

int main() {
    sol::state lua;
    lua.open_libraries(sol::lib::base);

    lua.set_function("run_coroutine", [](sol::function func) {
        sol::coroutine co = func;
        co();
        co();
        co();
    });

    lua.script(R"(
        function story()
            print("1")
            coroutine.yield()
            print("2")
            coroutine.yield()
            print("3")
        end

        run_coroutine(story)
    )");
}

The expected output is

1
2
3

but actually nothing is shown.

How can I correctly run the Lua function as a coroutine in C++?

Harumaki · Accepted Answer · 2024-09-14 09:34:33Z

Following the official example, I have resolved the issue myself, so I am posting the solution here.

#include <sol/sol.hpp>

int main() {
    sol::state lua;
    lua.open_libraries(sol::lib::base, sol::lib::coroutine);

    lua.set_function("run_coroutine", [&lua](sol::function f) {
        sol::thread runner_thread = sol::thread::create(lua);
        sol::state_view runner_thread_state = runner_thread.state();
        sol::coroutine co(runner_thread_state, f);

        co();
        co();
        co();
    });

    lua.script(R"(
        function story()
            print("1")
            coroutine.yield()
            print("2")
            coroutine.yield()
            print("3")
        end

        run_coroutine(story)
    )");
}

This should work now, but I’m not entirely sure why. I would appreciate it if someone with more knowledge about Lua threads could provide further insights.

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