One-to-many pattern in C++ 11 - Exploring std::reference_wrapper in the context of a pattern for a one-to-many relationship with ownership in C++. (See http://codereview.stackexchange.com/a/63821/53507)

One-to-many C++ Pattern

#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <string>
#include <iostream>

using namespace std;

class Question;

class User
{
public:
    ~User();
    
    void ask( Question& question )
    {
        questions.push_back( question );
    }

    void unAsk( const Question& question );
    
    const std::vector< std::reference_wrapper<Question> >& getQuestions( void ) const;
    std::vector< std::reference_wrapper<Question> >& getQuestions( void );


protected:
    std::vector< std::reference_wrapper< Question > > questions;
};

class Question
{
public:
    Question( User& user, int id ) : id(id), user( user ){  user.ask( *this ); }
    ~Question();
    void invalidate() {valid = false;}
    
    std::string text;
    
    const std::string getText() const {
        return text;
    }
    
    bool isEqual(const Question& q) const {
        return id == q.id;
    }
    
protected:
    int id;
    User& user;
    bool valid = true;
};



Question::~Question( void )
{
    user.unAsk( *this );
}

User::~User( void )
{
    for ( auto& question: questions ) {
        question.get().invalidate();
    }
}

void User::unAsk( const Question& question )
{
    //Something like this: remove_if(questions.begin(), questions.end(), [question](const Question& q) {return q.isEqual(question);});
    //Commented out the above line, wasn't very pertinent to question being explored, and it seems I'm making some silly mistake, so it isn't working.
}

const std::vector< std::reference_wrapper<Question> >& User::getQuestions( void ) const
{
    return questions;
}

std::vector< std::reference_wrapper<Question> >& User::getQuestions( void )
{
    return questions;
}

void function1( const User& user )
{
    user.getQuestions()[0].get().text = "should not be able to to edit question"; // compile error
}

void anotherFunction( User& user )
{
    user.getQuestions()[0].get().text = "edit question"; // just fine
}



int main(int argc, const char * argv[]) {
    User u1;
    Question q1(u1,1);
    q1.text = "What is 6 times 7 ?";
    anotherFunction(u1);
    function1(u1);
    
    cout << q1.getText() << endl;
    
    u1.unAsk(q1);
    
    return 0;
}