The Chain of Responsibility pattern is a behavioral design pattern that allows an object to pass a request along a chain of potential handlers until the request is handled or reaches the end of the chain. In C++, constructors play an important role in initializing the chain and setting up the relationships between handler objects.

Basic Constructor for Handler

In the Chain of Responsibility pattern, each handler in the chain is typically implemented as a separate class. The first step is to define a basic constructor for the handler class. This constructor will receive parameters to initialize the handler’s properties and to establish the next handler in the chain.

class Handler {
public:
    Handler(Handler* nextHandler) : nextHandler(nextHandler) {}

    // ...
private:
    Handler* nextHandler;
};

Concrete Handler Constructors

Next, you will need to implement constructors for each concrete handler class that inherits from the base Handler class. These constructors will call the base class constructor to set up the next handler in the chain.

class ConcreteHandlerA : public Handler {
public:
    ConcreteHandlerA(Handler* nextHandler) : Handler(nextHandler) {}

    // ...
};

class ConcreteHandlerB : public Handler {
public:
    ConcreteHandlerB(Handler* nextHandler) : Handler(nextHandler) {}

    // ...
};

Building the Chain

To build the chain of responsibility, you need to create instances of the concrete handler classes and connect them in the desired order. Here’s an example of how you can construct a chain of ConcreteHandlerA and ConcreteHandlerB objects:

int main() {
    // Create instances of the concrete handler classes
    ConcreteHandlerA handlerA(nullptr);
    ConcreteHandlerB handlerB(&handlerA);

    // Connect the handlers in the desired order
    handlerA.setNextHandler(&handlerB);

    // ...
    return 0;
}

In the example above, handlerA is connected to handlerB by passing a pointer to handlerB when constructing handlerA. Additionally, the setNextHandler method is invoked on handlerA to set handlerB as the next handler in the chain.

Conclusion

Constructors play a crucial role in setting up the chain of responsibility in the Chain of Responsibility pattern. By properly constructing and connecting the handler objects, you can create a flexible and scalable chain that handles requests in a systematic manner.

#ChainOfResponsibility #Constructor #CPlusPlus