Should accessors return values or constant references?

Question

Suppose I have a class Foo with a std::string member str. What should get_str return?

std::string Foo::ge         


        

Answer 1

I believe the second implementation (const reference) is correct as:

1. the returned object is immutable and therefore upholds the rules of encapsulation.
2. it's slightly more efficient as there is no copying of str.

However the first approach will work almost as well.