Unsubscribing multiple times

[samuelgruetter]

Quoting from an email by @headinthebox, to make sure we don't forget about this issue:

Another bug in RxJava/Scala

When you create a new subscription it does not remember that is is already disposed

In scala (using trivial companion object)

Val s = Subscription{ println(“hi”) }
s.unsubscribe()
s.unsubscribe()

prints “hi” twice, in .NET only once.

In the course I will tell the students it prints only once

The issue is already present in Java:

    public static void main(String[] args) {
        Subscription s = Subscriptions.create(new Action0() {
            public void call() {
                System.out.println("hi");
            }
        });
        s.unsubscribe();
        s.unsubscribe();
    }

also prints "hi" twice.

Let's fix this first in Java, and then add a companion object Subscription to RxScala.