Comment by fluoridation

>Let’s say I have a physics system that runs an update. Assume we catch outside the update. If anything throws the system is now in an intermediate state and is effectively irrecoverable.

That's a transaction kind of scenario. You catch at a recoverable point and rollback to a good state, and if that's not possible, then you simply fail out. I don't understand; what problem did exceptions introduce here? An exception was thrown (i.e. an error happened) during an intermediate operation and the operation as a whole stopped. What would have changed if every function had used error codes instead? It would have been either an error you were incapable of handling (in the sense that you didn't even look at the error code), and the operation would have silently continued in a possibly corrupted state, or it would have been an error you were capable of handling, in which case implement that same handling logic for the exception code.

  if (op1() != SUCCESS){
    //recover and continue
  }
  if (op2() != SUCCESS){
    //nothing to do so just fail out
    return FAIL;
  }
  //don't care about error so don't even bother checking
  (void)op3();
  //now the state of the program may be invalid
  op4();

becomes

  try{
    op1();
  }catch (/*...*/){
    //recover and continue
  }
  op2(); //let exception be caught by someone who can do something about it
  op3(); //same
  //sometimes we won't get here, but at least if we do, we know the state of the program is valid
  op4();

Is it just that you like ifs more than try-catches?

>If you want to argue that exceptions should only be used for irrecoverable errors such that the subsystem is not expected to resume then I would list.

That would depend on what you mean by "irrecoverable error". I interpret that to mean that the program cannot continue to function safely and it's better to terminate ASAP than to attempt to do anything else at all. If that's what you mean then no, that's not what exceptions are for. Like I said in a sibling comment (https://news.ycombinator.com/item?id=48527216), exceptions are meant to signal an error that may or may not be recoverable that the immediate caller may not know how to handle. Someone in the call stack should be able to decide based on program state how to respond to the error condition; sometimes that will involve rolling back to a valid state, as I said before, perhaps retrying; sometimes you will cancel the operation and discard the interrupted computation; sometimes you will notify the user or log an error; sometimes you will decide that there's actually nothing else for the program to do and clean up and exit.

>You tell me an example of a system that doesn’t use exceptions where adding exceptions makes it better.

Sure, no problem:

  if (op1() != SUCCESS)
    return FAIL;
  if (op2() != SUCCESS)
    return FAIL;
  if (op3() != SUCCESS)
    return FAIL;
  //etc.

with exceptions becomes

  op1();
  op2();
  op3();
  //etc.

All else being equal, exceptions make this kind of code better by making it more readable. If the non-exception code needs to return both error codes and partial values, it becomes even more noticeable:

  auto [result1, error1] = op1();
  if (error1 != SUCCESS)
    return FAIL;
  auto [result2, error2] = op2(result1);
  if (error2 != SUCCESS)
    return FAIL;
  auto [result3, error3] = op3(result2);

versus:

  op3(op2(op1()))