Subjects

A  Subject is an entity that is both an Observer and an Observable. It helps to relay notifications from one Observable (typically)  to a set of Observers. We can implement sophisticated techniques such as the caching and buffering of data using a Subject. We can also use a Subject to transform a hot Observable into a cold Observable. There are four variants of subjects implemented in RxCpp library. They are as follows:

• SimpleSubject
• BehaviorSubject
• ReplaySubject
• SynchronizeSubject

 

 

Let's write a simple program that will demonstrate the work of a Subject. The code listing will demonstrate how we can push data to a Subject and retrieve them using the Observer side of the Subject.

//------- SimpleSubject.cpp 
#include <rxcpp/rx.hpp> 
#include <memory> 
int main(int argc, char *argv[]) { 
    //----- Create an instance of Subject 
    rxcpp::subjects::subject<int> subject; 
    //----- Retreive the Observable  
    //----- attached to the Subject 
    auto observable ...