* bind can not be used with references, limiting the coroutine interface to don't use references is not a solution.
yes, I hoped to use bind to store new values in the parameters of coroutine-fn so that the user could still used the fn parameters as in a usual function,. unfortunately it does not work with references.
* access to the coroutine parameter using get, while it ensures a uniform and safe way to obtain them, is not easier to read, and in this case the coroutine function shouldn't follow the coroutine signature, which for some of you make the interface type unsafe.
seams to be a decision between 'tuple<> self_t::yield()' and void 'self_t::yield()' + 'T self_t::get<>()'. The design with get<>() is not hard to implement because I store already the tuple of fn parameters inside. Oliver