Can I use std::optional for error handling? [closed]

Question

With C++17 we got std::optional which is a useful wrapper for expressing nullable types.

Can I use it for error handling? It's quite appealing to do so:

optional<int> Compute()
{
  //... compute something valid...
  return std::nullopt; // error!
}

Would it be a good choice? Isn't it the same are returning a null pointer?

The problem, that people reports, is that you lose a message what happened in the case of an error. So returning some status code might be better.

other alternatives:

• std::variant<Value, errorCode>
• std::pair<Value, errorCode
• return error code and have a value as an output parameter
• throw an exception

Answer 1

I think std::optional is a great replacement for error handling code like that:

int GetAvailablePositiveNumber()
{
    if (condition)
        return 1;
    if (condition2);
        return 2;
    return -1;
}

int result = GetAvailablePositiveNumber();
if (result == -1)
{
    // We have no available positive numbers - handle error;
}

You will never need to use -1 ever again.

Also about the other alternatives you have mentioned, my answer is: the right tool for the right job. They have their own uses. Just pick the best tool on a case-by-case basis.