Passing vectors by reference

Question

If I have a vector of objects in one class which I want to change in another, I would try and pass all the information by reference.

What exactly do I need to pass by reference though? The vector? The objects? Both?

Essentially what I'm asking is: What is the difference between these?

vector&<object> blah; // A reference to a vector of objects?  vector<object&> blah; // A vector of references to objects?  vector&<object&> blah; // A reference to a vector of references to objects??? 

I'm not actually sure how referencing of array like containers work. Are these legal?

Answer 1

vector&<object> is a syntax error. vector<object&> is invalid, because a vector's value type must be assignable. vector&<object&> blah is a syntax error.

A reference to a vector is vector<T>&.

Answer 2

You cannot have a vector of references. Vector elements must be copyable and assignable, which references are not. So only the first option is actually an option, but it's spelled std::vector<Object> &.

Note that v[1] already returns a reference to the second element, so you can happily pass individual elements by reference.

_{It is possible to have a vector of reference-wrappers a la std::ref, but if you don't know what that is, you probably shouldn't be using it at this point.}