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copied!<p>You could write a class template <code>auto_iterator_impl</code> and use it through a function template <code>auto_iterator</code> which returns an instance of <code>auto_iterator_impl</code>, which can be implicitly converted into <code>true</code> or <code>false</code>:</p> <p>A working implementation with minimal functionalities and consideration:</p> <pre><code>template<typename C> struct auto_iterator_impl { C & c; typename C::iterator it; auto_iterator_impl(C & c, typename C::iterator & it) : c(c), it(it) {} operator bool() const { return it != c.end(); } typename C::iterator operator->() { return it; } }; template<typename C> auto_iterator_impl<C> auto_iterator(C & c, typename C::iterator it) { return auto_iterator_impl<C>(c, it); } </code></pre> <p>Test code:</p> <pre><code>void test(std::map<int, int> & m, int key) { if (auto x = auto_iterator(m, m.find(key))) { std::cout << "found = " << x->second << std::endl; x->second *= 100; //change it } else std::cout << "not found" << std::endl; } int main() { std::map<int,int> m; m[1] = 10; m[2] = 20; test(m, 1); test(m, 3); test(m, 2); std::cout <<"print modified values.." <<std::endl; std::cout << m[1] << std::endl; std::cout << m[2] << std::endl; } </code></pre> <p>Output:</p> <pre><code>found = 10 not found found = 20 print modified values.. 1000 2000 </code></pre> <p>Online demo : <a href="http://www.ideone.com/MnISh" rel="nofollow">http://www.ideone.com/MnISh</a></p>

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