pub struct MyActor {
    pub handler: Box<dyn Fn() -> Pin<Box<dyn Future<Output = ()>>> + Send + Unpin + 'static>,,
}

fn handler() -> Pin<Box<dyn Future<Output = ()>>> {
    Box::pin(async {})
}

pub trait Factory<T, R>: Clone + Unpin + 'static
where
    T: Unpin + 'static,
    R: Future<Output = ()>,
{
    fn call(&self, param: T) -> R;
}

impl<F, R> Factory<(), R> for F
where
    F: Fn() -> R + Clone + Unpin + 'static,
    R: Future<Output = ()>,
{
    fn call(&self, _: ()) -> R {
        (self)()
    }
}

pub struct Handler<F, T, R>
where
    T: Unpin + 'static,
    F: Factory<T, R>,
    R: Future<Output = ()>,
{
    pub hnd: F,
    _t: PhantomData<(T, R)>,
}

pub struct MyActor<F, T, R>
where
    F: Factory<T, R>,
    T: Unpin + 'static,
    R: Future<Output = ()> + Unpin + 'static,
{
    pub handler: Handler<F, T, R>,
}

async fn handler() {
    //...
}

error[E0277]: `from_generator::GenFuture<[static generator@src/main.rs:97:20: 99:2 {}]>` cannot be unpinned
  --> src/main.rs:91:18
   |
91 |     let actor0 = MyActor::new(handler).start();
   |                  ^^^^^^^^^^^^ within `impl futures::Future`, the trait `Unpin` is not implemented for `from_generator::GenFuture<[static generator@src/main.rs:97:20: 99:2 {}]>`
...
97 | async fn handler() {
   |                    - within this `impl futures::Future`
   | 
  ::: src/async_handler_type/actor/mod.rs:31:5
   |
31 |     pub fn new(handler: F) -> Self {
   |     ------------------------------ required by `MyActor::<F, T, R>::new`
   |
   = note: required because it appears within the type `impl futures::Future`
   = note: required because it appears within the type `impl futures::Future`

pub trait Factory<T, R>: Clone + Unpin + 'static

pub struct Handler<F>
where F: Future<Output = ()>,
{
    pub handler: Box<dyn Fn() -> F>,
}

pub struct MyActor<F>
where F: Future<Output = ()> + 'static,
{
    pub handler: Handler<F>,
}