documentation bug, create needs a template parameter.

[kirkshoop]

On the Gitter channel -
Peter Majchrak @petoknm Jul 09 09:54
i was missing a template parameter for create

auto ints = rxcpp::observable<>::create<int>( [](rxcpp::subscriber<int> s){ s.on_next(1); s.on_next(2); s.on_completed(); });

please update http://reactive-extensions.github.io/RxCpp/ to reflect that. thanks

[petoknm]

I think the template parameter can be inferred by the type of the lambda passed in... I see it being too verbose having a template parameter on create and on subscriber as well if they always match... I think that the way the documentation had it (without the template parameters) was cleaner and nicer

[kirkshoop]

Yes, that is true when using the type-forgetting subscriber<T>. Perhaps a different create overload could be added for that, but then create would have a different usage depending on the type of the parameter declared in the lambda. That seems too subtle to communicate to users.

Thoughts?

[petoknm]

What exactly do you mean by "type forgetting subscriber<T>"? and what exactly would the difference in usage be?

[kirkshoop]

std::function<> is type-forgetting. It uses virtual functions and heap allocation to hide the type of the function that was passed to its constructor. This allows it to be used as a parameter or struct member that can hold a variety of function implementations; lambda, object, function ptr, etc..

subscriber<T, Implementation> is the full type of subscriber. This can be efficient, because no heap alloc or virtual functions are required. When subscriber<T> is used the Implementation uses virtual functions and heap alloc to hide the real Implementation type.

type-forgetting is expensive and should be used only when needed.

If a create overload was added to remove the template param when using type-forgetting it would look like this.

auto ints = rxcpp::observable<>::create( [](rxcpp::subscriber<int> s){ s.on_next(1); s.on_next(2); s.on_completed(); });

However, the existing overload would still be needed when the type is not forgotten.

auto ints = rxcpp::observable<>::create<int>( [](auto s){ s.on_next(1); s.on_next(2); s.on_completed(); });

There is no way that create could extract int from the auto param of the lambda.