Question

Suppose I have a static method of my class that returns an object of the same type of my class. To create the object for example this method have to parse a string:

class C
{
public:

   static C get_obj(const std::string& str)
   {
      C obj;
      // Parse the string and set obj properties
      return obj;
   }
};

If, when I parse the string, I get an error and the object can’t be constructed as a valid object, have I to throw an exception or what else?

Answer 1

Given that there is a possibility of failure in get_obj the failure must be reported back to the caller in some manner. This is typically either done by

• Throwing an exception
• Communicating the failure in the output of the method

In this particular case the only output of the method is a C instance. Given that throwing an exception is probably the best option for a method of this signature. The only other choice is to embed the success / failure inside the C object which you almost certainly don’t want to do.

Another way to approach this problem is the try_parse pattern. Let a bool return indicate success / failure and return the constructed object on success through a reference parameter

bool try_parse(const std::string& str, C& obj) {
  if (string is valid) { 
    obj = C(...);
    return true;
  }

  return false;
}