Is return_internal_reference efficient?

### Is `return_internal_reference` efficient?

Q: /I have an object composed of 12 doubles. A `const&` to this object is returned by a member function of another class. From the viewpoint of using the returned object in Python I do not care if I get a copy or a reference to the returned object. In Boost.Python I have the choice of using `copy_const_reference` or `return_internal_reference`. Are there considerations that would lead me to prefer one over the other, such as size of generated code or memory overhead?/

A: `copy_const_reference` will make an instance with storage for one of your objects, `size = base_size + 12 * sizeof(double)`. `return_internal_reference` will make an instance with storage for a pointer to one of your objects, `size = base_size + sizeof(void*)`. However, it will also create a weak reference object which goes in the source object's weakreflist and a special callback object to manage the lifetime of the internally-referenced object. My guess? `copy_const_reference` is your friend here, resulting in less overall memory use and less fragmentation, also probably fewer total cycles.