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    <p>The problem here seems more a problem of design than a problem of swap.</p> <p>You (basically) use a pointer to a variable you did not assign yourself as an identifier of the kid... so of course as soon as the kids are moved around, it's going to break. (well it's slightly better than a pointer actually, but not by much)</p> <p>You have 2 solutions:</p> <ul> <li>the basic > instantiate them yourselves</li> <li>the more complicated > factory + id</li> </ul> <p>And of course you also have the problem that you tied up <code>Home</code> and its implementation... but I'll let you write a proper <code>Home</code> class by yourself. By the way, since the number of templates parameters of a STL container depend both on the container and on the actual implementation of the STL you are using, your solution is far less generic than using a real class ;)</p> <p><strong>Basic</strong>:</p> <pre><code>class kid { public: kid(kid* related = 0): m_related(related) {} // methods private: // other attributes kid* m_related; }; int main(int argc, char* argv[]) { Home home1, home2; kid* kid1 = home1.insert(new kid(home1, 1)); home1.insert(new kid(home1, 2, kid1)); kid* kid2 = home2.insert(new kid(home2, 1)); kid* kid3 = home2.insert(new kid(home2, 2)); home.insert(new kid(home2, 3, kid2)); home.insert(new kid(home2, 4, kid3)); swap(home1,home2); // just swapping the vectors, since it only moves pointers not the objects } </code></pre> <p>That's the easy way, but of course I still curse you because I have 2 kids with an id of 1...</p> <p><strong>Factory</strong></p> <pre><code> class KidFactory; class KidKey { friend class KidFactory; KidKey() {} }; class Kid { public: Kid(KidKey, Id id, Id cousinId); Id getId() const { return m_id; } const Home* getHome() const; void setHome(const Home&amp; home); private: const Home* m_home; Id m_id; Id m_cousinId; }; // Factory class KidFactory { public: Kid&amp; createKid(Id cousinId = -1) { m_kids.push_back(Kid(KidKey(), m_kids.size(), cousinId)); return m_kids.back(); } Kid&amp; getKid(Id id) { return m_kids.at(id); // notice that might generate out_of_range exception } private: std::vector&lt;Kid&gt; m_kids; }; class Home { public: void insert(Kid&amp; kid) { m_kids.push_back(kid.getId()); kid.setHome(*this); } }; int main(int argc, char* argv[]) { KidFactory factory; Home home1, home2; home1.insert(factory.createKid()); home1.insert(factory.createKid(home1.front().getId())); Kid&amp; kid1 = factory.createKid(); home2.insert(kid1); home2.insert(factory.createKid(kid1.getId())); // once again swapping vectors is fine } </code></pre> <p>Proper design leads to easy to write code... but some boilerplate one in C++ :(</p>
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    1. POswapping container with self referencing element
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    1. USMatthieu M.
    1. USMatthieu M.
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    1. COI am not sure whether this is proper design. The first method doesn't solve the problem specified, it creates kid using new. and with arbitrary set of stable pointers one can always put a pointer to cousin. For the second one, it just violets encapsulation. kid should not give his home address to public, someone could kidnap them. general public are also not allowed to set home for a kid. What will happen if some bad guy comes and set his home to a different locality, but not for his cousin. All the kids will get confused and point out to wrong cousin, just as it happens in my code.
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      1. USabir
    2. COrightly said by abir, getHome and setHome must be private if they are ever needed really.
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    3. COI demonstrate a principle, you criticize a detail... Without knowing about your application, how can I say who is responsible for setting the Home of a new Kid ? It's your job to decide this, not mine, I never intended to do your job for you.
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