Null object Logger

null.cpp

#include <iostream>
#include <string>

// Logger Interface
class Logger {
public:
    virtual void log(const std::string& message) = 0;
    virtual ~Logger() {}
};

// RealLogger - A concrete implementation of Logger
class RealLogger : public Logger {
public:
    void log(const std::string& message) override {
        std::cout << "Logging message: " << message << std::endl;
    }
};

// NullLogger - The Null Object Implementation
class NullLogger : public Logger {
public:
    void log(const std::string& message) override {
        // No operation performed, acts as a null object
    }
};

// Application class that uses Logger
class Application {
private:
    Logger* logger;

public:
    // Constructor that takes a logger, defaulting to NullLogger if null
    Application(Logger* _logger) : logger(_logger) {}

    void run() {
        // In the actual logic, you don't need to check if logger is null.
        logger->log("Application started");
        // More application code...
        logger->log("Application finished");
    }
};

int main() {
    // Example 1: Using a RealLogger
    RealLogger* realLogger = new RealLogger();

    Application appWithRealLogger(realLogger);
    appWithRealLogger.run();  // This will log actual messages

    std::cout << "---------------------------" << std::endl;

    // Example 2: Using NullLogger (No logging will occur)
    NullLogger* nullLogger = new NullLogger();
    Application appWithNullLogger(nullLogger);  
    appWithNullLogger.run();  // No logging occurs

    return 0;
}