Self-contained Systems - C++

The Self-Contained System pattern aims to minimize dependencies between components by encapsulating all necessary resources within a single unit. This promotes modularity, testability, and reusability. Here, we demonstrate this with a simple Logger class that manages its own output stream. Instead of relying on a global stream or passing one in, the logger creates and uses its own ofstream. This makes the logger independent and easier to reason about. The implementation uses RAII (Resource Acquisition Is Initialization) with the ofstream to ensure the file is properly closed when the Logger object goes out of scope, a common and preferred C++ practice for resource management.

#include <iostream>
#include <fstream>
#include <string>

class Logger {
public:
  Logger(const std::string& filename) : file_(filename) {
    if (!file_.is_open()) {
      std::cerr << "Error opening log file: " << filename << std::endl;
    }
  }

  void log(const std::string& message) {
    if (file_.is_open()) {
      file_ << message << std::endl;
      file_.flush(); // Ensure immediate writing
    }
  }

  ~Logger() {
    if (file_.is_open()) {
      file_.close();
    }
  }

private:
  std::ofstream file_;
};

int main() {
  Logger logger("application.log");
  logger.log("Application started.");
  logger.log("Performing some operation...");

  return 0;
}