The Old New Thing

Using fibers to expand a thread’s stack at runtime, part 4
Last time, we transported some ephemeral error state from the temporary fiber to the originating thread. A common way of reporting an error in C++ is to use an exception, so let's use that. In this case, we capture the result of the callback with a std::variant of an exception_ptr or the formal return value. The exception_ptr is used if th