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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <memory>
  4. using namespace std;
  5.  
  6. template<typename T> struct foo {
  7.     virtual foo& operator<<(const T& e) const { std::cout << "check foo\n"; }
  8. };
  9.  
  10. struct derived : foo<int> {
  11.     virtual derived& operator<<(const int& e) const { std::cout << "check derived\n"; }
  12. };
  13.  
  14. template<typename T> struct genericDerived : foo<T> {
  15.     virtual derived& operator<<(const T& e) const { std::cout << "check genericDerived\n"; }
  16. };
  17.  
  18. //////
  19.  
  20. namespace detail
  21. {
  22. 	template<typename Foo, typename T>
  23. 		const std::shared_ptr<Foo>& dispatch_lshift(const std::shared_ptr<Foo>& o, const T& e, const std::true_type& enabler)
  24. 		{
  25. 			*o << e;
  26. 			return o;
  27. 		}
  28. }
  29.  
  30. template<typename Foo, typename T>
  31. const std::shared_ptr<Foo>& operator<<(const std::shared_ptr<Foo>& o, const T& e)
  32. {
  33. 	return detail::dispatch_lshift(o, e, std::is_convertible<Foo*, foo<T>* >());
  34. }
  35.  
  36. int main()
  37. {
  38. 	auto f = make_shared<foo<int>>();
  39. 	f << 1;
  40.  
  41. 	auto d = make_shared<derived>();
  42. 	d << 2;
  43.  
  44. 	auto g = make_shared<genericDerived<int>>();
  45. 	g << 3;
  46.  
  47. 	auto x = make_shared<int>();
  48. 	// x << 4; // correctly FAILS to compile
  49. }
  50.  
Success #stdin #stdout 0s 2968KB
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stdin
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Standard input is empty
stdout
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check foo
check derived
check genericDerived
https://ideone.com/26nqr
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
secret

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