doSubscribe

struct TestObserver
{
    void put(int n)
    {
    }
}

struct TestObservable1
{
    alias ElementType = int;
    Disposable subscribe(Observer!int observer)
    {
        return null;
    }
}

struct TestObservable2
{
    alias ElementType = int;
    Disposable subscribe(T)(T observer)
    {
        return null;
    }
}

TestObservable1 o1;
auto d0 = o1.doSubscribe((int n) {  }, () {  }, (Exception e) {  });
auto d1 = o1.doSubscribe((int n) {  }, () {  });
auto d2 = o1.doSubscribe((int n) {  }, (Exception e) {  });
auto d3 = o1.doSubscribe((int n) {  });
auto d4 = o1.doSubscribe(TestObserver());
TestObservable2 o2;
auto d5 = o2.doSubscribe((int n) {  }, () {  }, (Exception e) {  });
auto d6 = o2.doSubscribe((int n) {  }, () {  });
auto d7 = o2.doSubscribe((int n) {  }, (Exception e) {  });
auto d8 = o2.doSubscribe((int n) {  });
auto d9 = o2.doSubscribe(TestObserver());