doSubscribe

struct TestObservable
{
    alias ElementType = int;

    auto subscribe(TObserver)(TObserver observer)
    {
        .put(observer, [0, 1, 2]);
        return NopDisposable.instance;
    }
}

TestObservable observable;
int[] result;
observable.doSubscribe!(n => result ~= n);
assert(result.length == 3);

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());