Re: Are so many subclasses such a good idea?

The C++ exception handling mechanism is very expressive. I personally
like it a lot. Here is another example. Take a mutex class which can
throw exceptions. Here is one way to write it:
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class mutex_with_exceptions {
 pthread_mutex_t m_mtx;

 [...];

public:
 struct error {
   struct base {};

   struct lock {
     struct base : public error::base {};
     struct invalid : public lock::base {};
     struct priority_violation : pubilc lock::invalid {};
     struct deadlock : public lock::base {};
     struct max_recursion : public lock::base {};

     static void raise_status(int const status) {
       switch (status) {
         case EINVAL:
           throw priority_violation();
         case EAGAIN:
           throw max_recursion();
         case EDEADLK:
           throw deadlock();
         default:
           assert(false);
           std::unexpected();
       }
     }
   };

   struct unlock {
     struct base : public error::base {};
     struct not_owner : public unlock::base {};

     static void raise_status(int const status) {
       switch (status) {
         case EPERM:
           throw not_owner();
         default:
           assert(false);
           std::unexpected();
       }
     }
   };
 };

public:
 void lock() {
   int const status = pthread_mutex_lock(&m_mtx);
   if (status) {
     error::lock::raise_status(status);
   }
 }

 void unlock() {
   int const status = pthread_mutex_unlock(&m_mtx);
   if (status) {
     error::unlock::raise_status(status);
   }
 }
};

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The exception hierarchy for the `mutex_with_exceptions' class is verbose.

Any thoughts?