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

You can compose your class of members that take care of those restrictions but are assignable themselves.

#include 

template 
class readonly_wrapper
{
    T value;
public:
    explicit readonly_wrapper(const T& t): value(t) {}
    const T& get() const { return value; }
    operator const T& () const { return value; }
};

struct Foo{};

struct Bar {
  Bar (Foo & foo, int num) : foo_reference(foo), number(num) {}
private:
  std::reference_wrapper foo_reference;  //C++11, Boost has one too
  readonly_wrapper number;
  // Mutable member data elided
};

#include 
int main()
{
  std::vector bar_vector;
  Foo foo;
  bar_vector.push_back(Bar(foo, 10));
};