error[E0599]: no method named `poll` found for type `Fut` in the current scope
  --> src/stream/stream/successor.rs:51:52
   |
51 |         match self.as_mut().successor()(self.next).poll(cx) {
   |                                                    ^^^^ method not found in `Fut`
   |
   = help: items from traits can only be used if the type parameter is bounded by the trait
help: the following trait defines an item `poll`, perhaps you need to restrict type parameter `Fut` with it:
   |
41 | impl <F, Fut: core::future::future::Future, T> Stream for Successor<F, Fut, T>
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^