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  1. #include <iostream>
  2. #include <utility>
  3. using namespace std;
  4.  
  5. template<typename X>
  6. struct thing {
  7. };
  8.  
  9.  
  10. template<typename> struct traits {};
  11. template<
  12.  template<class>class T,
  13.  typename A>
  14. struct traits<T<A>> {
  15.  using param = A;
  16.  template<typename X>
  17.  using templ = T<X>;
  18. };
  19.  
  20.  
  21. template<typename Y>
  22. decltype (auto) g(Y&& t) {
  23.  // This is ugly, but well ...
  24.  using trait = traits<typename std::remove_reference<Y>::type>;
  25.  using A = typename trait::param;
  26.  // using it, not as simple as T<A>, but at least it works
  27.  typename trait::template templ<A> copy{t};
  28.  typename trait::template templ<void> other;
  29.  A data;
  30.  return std::forward<Y>(t);
  31. }
  32.  
  33. int main(int, char**) {
  34.  thing<int> it {};
  35.  g(thing<int> {});
  36.  g(it);
  37.  return 0;
  38. }
Success #stdin #stdout 0s 3408KB
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https://ideone.com/6yyiGw
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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