Returning reference to local temporary object

Question

This code

virtual const core::matrix4& getViewMatrixAffector() const {return core::matrix4();};

results with a warning telling me "Returning reference to local temporary object"...

How to solve this warning?

As mentioned below i tried to remove the '&'...

Answer 1

When you create an object as a local temporary, it is destroyed as soon as the function's scope ends. In turn, you should never return a reference to it, as this would yield Undefined Behaviour. Consider returning it by value, or returning a smart pointer to an object on the free store.

Answer 2

Since you're not in control of the return type, you must make sure you return a valid object and not just a temporary. One solution would be a function-local static variable:

virtual const core::matrix4& getViewMatrixAffector() const
{
  static const core::matrix4 val;
  return val;
};

If you find yourself doing this in many functions (with the same type of the variable), make val a (suitably renamed) static member of the class.