Question

What is the exact difference between having myMethod(Thing& a) or myMethod(Thing a)? Because later you still ned to use &a if you want the address of the object.. I’m not sure when to use what..

Answer 1

Three differences:

1. With a reference, you have a “shared” instance. So if you modify a you change the original and vice versa.
2. Performance. With Thing a you invoke the copy constructor. If the copy constructor has to do a lot of things, that could affect how fast the code runs.
3. A reference is guaranteed to work. If the class has a private copy constructor, you will not be able to do Thing a but you can always do Thing &a.

Finally, if you don’t intend for the caller to be able to change the underlying object, you should probably pass by const reference (const Thing &a)