gistfile1.rs

trait Subscriber<Input> {
    fn on_subscribe(&self, s: &Subscription);
    fn on_next(&self, t: Input);
    fn on_error(&self, err: String);
    fn on_complete(&self);
}

// how do I explain that Subscriber will outlive O and SingleStrategy as well?  e.g. we can almost assume that Subscriber is static, // but not quite. 

struct SingleStrategy<O> {
    subscriber: Option<(Subscription, Subscriber<O>)>
}