Simply put, reactive programming is nothing but programming with asynchronous data streams. By applying various operations on stream, we can achieve different computational goals. The primary task in a reactive program is to convert data into streams, regardless of what the source of the data is. While writing modern graphical user interface applications, we process mouse move-and-click events. Currently, most systems get a callback and process these events as and when they happen. Most of the time, the handler does a series of filtering operations before it invokes the action methods associated with the event calls. In this particular context, reactive programming helps us in aggregating the mouse move-and-click events into a collection and sets a filter on them before notifying the handler logic. In this way, the application/handler logic does not get executed unnecessarily.

The stream-processing model is well known, and it is very easy to encode by application developers. Pretty much anything can be converted into a stream. Such candidates include messages, logs, properties, Twitter feeds, blog posts, RSS feeds, and so on. Functional programming techniques are really good at processing streams. A language such as Modern C++, with excellent support for Object/Functional programming, is a natural choice for writing reactive programs. The basic idea behind reactive programming is that there are certain datatypes that represent a value over time. These datatypes (or rather data sequences) are represented as Observable sequences in this programming paradigm. Computations that involve these changing (time-dependent) values will, in turn, themselves have values that change over time, and will need to asynchronously receive notifications (as and when the dependent data changes).