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  1. #include <iostream>
  2. #include <type_traits>
  3. using namespace std;
  4.  
  5. template<typename FROM, typename TO>
  6. struct CopyConstImpl {
  7. 	using type = typename std::remove_const<TO>::type;
  8. };
  9.  
  10. template<typename FROM, typename TO>
  11. struct CopyConstImpl<const FROM, TO> {
  12. 	using type = typename std::add_const<TO>::type;
  13. };
  14.  
  15. template<typename FROM, typename TO>
  16. struct CopyConst {
  17. 	using type = typename CopyConstImpl<typename std::remove_reference<FROM>::type, TO>::type;
  18. };
  19.  
  20. struct Foo {
  21.   int& bar() { return barImpl(*this); }
  22.   const int& bar() const { return barImpl(*this); }
  23. private:
  24.   template<typename THIS>
  25.   static auto barImpl(THIS&& instance) -> typename CopyConst<THIS, int>::type& {
  26.   	return instance.x;
  27.   }
  28.   int x = 5;
  29. };
  30.  
  31. int main() {
  32. 	static_assert(is_same<int&, decltype(declval<Foo>().bar())>::value,
  33. 		"Non-const foo.bar() result must yield a non-const reference");
  34. 	static_assert(is_same<const int&, decltype(declval<const Foo>().bar())>::value,
  35. 		"Const foo.bar() result must yield a const reference");
  36.  
  37. 	return 0;
  38. }
Success #stdin #stdout 0s 3136KB
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https://ideone.com/PW0vK4
inout on this
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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