How to copy (or swap) objects of a type that contains members that are references or const?

Question

The problem I am trying to address arises with making containers such as an std::vector of objects that contain reference and const data members:

Answer 1

that const member really should be const

Well, then you can't reassign the object, can you? Because that would change the value of something that you've just said really should not change: before the assigment foo.x is 1 and bar.x is 2, and you do foo = bar, then if foo.x "really should be const" then what's supposed to happen? You've told it to modify foo.x, which really should not be modified.

An element of a vector is just like foo, it's an object that the container sometimes modifies.

Pimpl might be the way to go here. Dynamically allocate an object (the "impl") containing all your data members, including const ones and references. Store a pointer to that object (the "p") in your object that goes in the vector. Then swap is trivial (swap the pointers), as is move assignment, and copy assignment can be implemented by constructing a new impl and deleting the old one.

Then, any operations on the Impl preserve the const-ness and un-reseatable-ness of your data members, but a small number of lifecycle-related operations can act directly on the P.