case dropped(Element)The stream didn’t enqueue the element because the buffer was full.
case terminatedThe stream didn’t enqueue the element because the stream was in a terminal state.
Discussion 解説
This value represents the successful enqueueing of an element, whether the stream buffers the element or delivers it immediately to a pending call to next(). The associated value remaining is a hint that indicates the number of remaining slots in the buffer at the time of the yield call.