Converting connectable_observable* to observable*

[martinfinke]

Please consider this example:

// 1: This compiles
rxcpp::connectable_observable<int> connectable;
rxcpp::observable<int> o = connectable;

// 2: This doesn't
rxcpp::connectable_observable<int> *connectable_ptr;
rxcpp::observable<int> *ptr = connectable_ptr;

Since connectable_observable derives from observable, why does (1) compile, and (2) doesn't?

[kirkshoop]

Yes, connectable_observable<> does inherit from observable<>

template<class T, class SourceOperator>
class connectable_observable
    : public observable<T, SourceOperator>

The devil is in the type-forgetting of the SourceOperator.

template<
    class T = void,
    class SourceObservable = typename std::conditional<std::is_same<T, void>::value,
        void, dynamic_observable<T>>::type>
class observable;

template<class T,
    class SourceObservable = typename std::conditional<std::is_same<T, void>::value,
        void, dynamic_connectable_observable<T>>::type>
class connectable_observable;

So connectable_observable<int> is actually

class connectable_observable<int, dynamic_connectable_observable<int>>
    : public observable<int, dynamic_connectable_observable<int>>

which does not convert to observable<int, dynamic_observable<int>>

This is surprising behavior and we should think about how to make the type-forgetting work with this cast to the base.

Thanks for the report!