Le 13/09/12 18:39, Eugene Yakubovich a écrit :
This design required pre-fetching and storing the return value via a context jump into the generator routine. Only with this mechanism I was able to know if the next call to generator<>::operator() will return a value. (requires that the first pre-fetch is done in the ctor of generator<>
The difference to the actual design
if ( optional< int > val = gen() ) { .... }
is that I don't need to pre-fetch and not to store the optional<> as parameter (optional is only created inside generator<>::operator()).
If the generator-function returns non-void (original design) and has no yield_break, then it's possible for generator::operator() to return R (not optional<R>) and do no prefetching. But personally, I would rather take the optional<R> with a void generator-function and provide the iterator (iterator::operator* will return R, not optional<R>) as the preferred interface. +1.
* The access to the actual coroutine parameters is asymmetric, letting access to old actual parameters that can point to objects that have already been destroyed.
Maybe the self_t object could take care of this (or this_coroutine). We can use a get<> function to give access to the actual parameters.
int f20(coro_t::self_t & self) { self.yield(2*self.get<0>()); }
int f20() { typedef this_coroutine<int(int)> this_coro; this_coro::yield(2*this_coro::get<0>()); } interesting idea, I find it better than the version using bind because you don't can't forget to 'bind'. you are always required to use self_t::get<>(). One could still do this:
int f20(coro_t::self_t & self) { X& x1 = self.get<0>(); self.yield(); X& x2 = self.get<0>(); // use x1 and x2 here. x1 might be bogus now } You are right. This is why I prefer the bind approach, if doable. Maybe the example is a bit contrived but not anymore than the original one where the use of formal parameters posed the same danger. Even with bind(), one could create a ref/ptr to the bound variable that would be bogus after the next yield(). I don't see the problem with bind. Could you show an example?
Best, Vicente