Common Use Cases for mutable

1#include <iostream>
2
3class Calculator {
4 public:
5  int Calculate() const {
6    if (!cacheValid) {
7      cachedResult = PerformExpensiveCalculation();
8      cacheValid = true;
9    }
10    return cachedResult;
11  }
12
13 private:
14  int PerformExpensiveCalculation() const {
15    return 42;  // Example calculation
16  }
17
18  mutable int cachedResult{0};     
19  mutable bool cacheValid{false};  
20};
21
22int main() {
23  Calculator calc;
24  std::cout << calc.Calculate() << '\n';
25}

1#include <iostream>
2
3class Logger {
4 public:
5  void Log() const {
6    ++logCount;  
7    std::cout << "Logging action #"
8      << logCount << '\n';
9  }
10
11 private:
12  mutable int logCount{0};  
13};
14
15int main() {
16  Logger logger;
17  logger.Log();
18  logger.Log();
19}

1#include <iostream>
2#include <mutex>
3
4class ThreadSafeCounter {
5 public:
6  void Increment() const {
7    std::lock_guard<std::mutex> lock(mutex);  
8    ++count;
9  }
10
11  int GetCount() const {
12    std::lock_guard<std::mutex> lock(mutex);  
13    return count;
14  }
15
16 private:
17  mutable int count{0};      
18  mutable std::mutex mutex;  
19};
20
21int main() {
22  ThreadSafeCounter counter;
23  counter.Increment();
24  std::cout << "Counter: " << counter.GetCount();
25}