Should Exceptions Be Thrown from Constructors?

Throwing Exceptions from Constructors: Design Considerations

In the realm of software development, the debate persists regarding the propriety of throwing exceptions from constructors. This question has sparked discussion among programming enthusiasts, and a colleague's recent inquiry prompted us to delve into the topic.

Is it acceptable to throw exceptions from constructors from a design standpoint?

Consider a scenario where a class encapsulates a POSIX mutex, as illustrated in the example below:

class Mutex {
public:
  Mutex() {
    if (pthread_mutex_init(&mutex_, 0) != 0) {
      throw MutexInitException();
    }
  }
};

In this instance, if the call to pthread_mutex_init fails, the mutex object becomes unusable. Throwing an exception ensures that the object is not created in an inconsistent state, preventing potential errors down the road.

Standard Practice vs. Member Function Approach

One might argue that instead of throwing an exception, the class could have a member function for initialization that returns a boolean based on the result of the pthread_mutex_init call. This approach has its merits but introduces a subtle issue. It relies on every user remembering to invoke the initialization function, which can be overlooked and lead to undefined behavior. This deviation from the RAII principle (Resource Acquisition Is Initialization) can compromise the object's intended design.

Conclusion

While both approaches have their advantages, throwing exceptions from constructors has emerged as the standard. By failing early, it safeguards against creating incomplete or inconsistent objects, ensuring that the object's state is valid before any further operations are performed.

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