The purpose of this chapter is to introduce readers to the key interfaces of the reactive programming mode they are—IObservable<T> and IObserver<T>. They are in fact the duals of the IEnumerable<T> and IEnumerator<T> interface. We learned how to model those interfaces in classic C++ (well, mostly) and had toy implementations of all of them. Finally, we implemented a GUI program that captures mouse movements and notifies a list of Observers. These toy implementations are to get our feet wet with the ideas and ideals of the Reactive programming model. Our implementations can be considered as implementing of OOP-based reactive programming.
To be proficient in C++ reactive programming, a programmer has to be comfortable with the following topics:
- Advanced linguistic constructs provided by Modern C++
- Functional programming constructs provided by Modern C++
- Asynchronous programming (RxCpp handles it for you!) model
- Event stream processing
- Knowledge of industrial-strength libraries such as RxCpp
- Applications of RxCpp in GUI and web programming
- Advanced reactive programming constructs
- Handling errors and exceptions
This chapter was mostly about key idioms and why we require a robust model for handling asynchronous data. The next three chapters will cover language features of Modern C++, handling concurrency/parallelism with C++ standard constructs, and lock-free programming (made possible by memory model guarantees). The preceding topics will give the user a firm foundation from which to master functional reactive programming.
In Chapter 5, Introduction to Observables, we will once again return to the topic of Observables and implement interfaces in a functional manner to reiterate some of the concepts. In Chapter 6, Introduction to Event Stream Programming Using C++, we will move towards the advanced event stream processing topics with the help of two industrial-strength libraries that use the Domain Specific Embedded Language (DSEL) approach towards event stream processing.
By now, the stage will be set for the user to be exposed to the industrial-strength RxCpp library and its nuances to write professional-quality Modern C++ programs. In Chapter 7, Introduction to Data Flow Computation and the RxCpp Library and Chapter 8, RxCpp – the Key Elements, we will cover this wonderful library. The following chapters will cover Reactive GUI programming using the Qt library and advanced operators in RxCpp.
The last three chapters cover advanced topics of Reactive design patterns, micro-services in C++, and handling errors/exceptions. By the end of the book, the reader who started with classic C++ will have covered a lot of ground, not only in writing Reactive programs but in the C++ language itself. Because of the nature of the topic, we will cover most of the features of C++ 17 (at the time of writing).
