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copied!<p>This works, though is somewhat nasty:</p> <pre><code>#include <string> #include <iostream> class A { public: std::string msg; A(std::string s) { msg = s;} void filter() { std::cout << "Message A = " << msg << std::endl;} }; class B { public: std::string msg; B(std::string s) { msg = s;} void filter() { std::cout << "The B message: " << msg << std::endl;} }; // ------------- class Base { public: virtual void filter() = 0; virtual ~Base() {} }; template<class C> class Wrapper: public Base { public: Wrapper( C * impl ): m_impl(impl) { } ~Wrapper() { delete m_impl; } virtual void filter() { m_impl->filter(); } private: C * m_impl; }; // ------------- int main() { Base * f = NULL; int type = 1; switch (type) { case 1: f = new Wrapper<A>(new A("hi from A")); break; case 2: f = new Wrapper<B>(new B("hello from B")); break; } f->filter(); delete f; } </code></pre> <hr> <p>And the C++11, exception-safe variant with perfect forwarding of the constructors. Just <code>Wrapper</code> and <code>main()</code> are different from above, here they are:</p> <pre><code>template<typename T> class Wrapper : public Base { public: template<typename... Args> Wrapper(Args&&... args) : m_impl(std::forward<Args>(args)...) {} virtual void filter() { m_impl.filter(); } private: T m_impl; }; // ------------- int main() { std::unique_ptr<Base> f; int type = 1; switch (type) { case 1: f.reset(new Wrapper<A>("hi from A")); break; case 2: f.reset(new Wrapper<B>("hello from B")); break; } f->filter(); } </code></pre>

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