Polymorphic use of templates

Question

Here, the context of polymorphic is expecting 'Derived' from 'Base&. Given class P { }; class Q : public P { }; auto operator + (const P& p, int x) -> DYNAMIC_DECLTYPE(P) { DYNAMIC_DECLTYPE(P) p2(p); p2.func(x); return p2; } Is there a way to have DYNAMIC_DECLTYPE working? I want to use this form instead of template T operator + (const T& t, int x) or have a potentially long list of if (!strcmp(typeid(p).name(), typeid(derived()).name()) { ... } because the latter cannot be used to restrict T to P or subclasses thereof (prove me wrong, if possible). JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

What you are trying to do is in every sense of the word a template pattern: You have an unbounded family of return types with matching function argument types. This should simply be a straight template. If you want to restrict the permissible types, you should add some typetrait magic. Perhaps like this: #include template typename std::enable_if::value, T>::type operator+(T const & t, int x) { T s(t); s.func(x); return s; } (If func returns a reference, you can shortcut this to return T(t).func(x);.)