Immutable container with mutable content

Question

The story begins with something I thought pretty simple :

I need to design a class that will use some STL containers. I need to give users of the class access to an

Answer 1

The painful solution:

/* YOU HAVE NOT SEEN THIS */
struct mutable_int {
    mutable_int(int v = 0) : v(v) { }
    operator int(void) const { return v; }
    mutable_int const &operator=(int nv) const { v = nv; return *this; }

    mutable int v;
};

Excuse me while I have to punish myself to atone for my sins.