2025-09-11 13:21, Avi Kivity via Std-Proposals:

The Standard says

If searches for the names return_void and return_value in the scope

of the promise type each find any declarations, the program is ill-

formed.

However, there are cases where one wants both "co_return;" and

co_return something;" statements in the same coroutine.

The cases are when the coroutine returns a sum type such as std::future

or std::expected, and one of the options is void (e.g.

std::future<void> or std::expected<void, something>. In these cases,

one would want

Do you mean that you want it selectable at runtime depending on if the

`std::expected` contains the expected, void, or `something´? How would

that look in an example (that is accepted by an earlier version of gcc)?

future<> my_coroutine(int x) {

    if (x < 0) {

        co_return make_exception_future(std::invalid_argument());

    }

    // do some work

    co_return;

}

A working example at godbolt would be nice to see it in action.

Otherwise, isn't that what _constexpr-if_ solves?

Best regards,

Ted Lyngmo