How can I define struct that holds futures of function which functions will return a future

help
9 
async fn fn_name () {
  async { || {

  }}
}

type CallbackType = Pin<Box<dyn Future<Output = (bool, Option<Box<dyn Fn() -> ()>>)>>>

struct Functions {
  func: Vec<Pin<Box<CallbackType>>>
}

impl Functions {
  fn add (&mut self, callback: fn() -> CallbackType) {
    self.func.push(Box::pin(callback));
  }  
}

let f = Functions{...};
f.add(fn_name)

now when I call the name function its showing expected struct Pin, found opaque type this error.