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  1. #include <memory>
  2. #include <type_traits>
  3.  
  4. struct unused;  // forward declaration only
  5.  
  6. template<class Container>
  7. using const_ref_if_copy_constructible = typename std::conditional<
  8.         std::is_copy_constructible<typename Container::value_type>::value,
  9.         Container const&,
  10.         unused>::type;
  11.  
  12. template<typename T>
  13. class Container {
  14.     T t;
  15. public:
  16. 	typedef T value_type;
  17.  
  18.     Container() = default;
  19.  
  20. 	Container(const_ref_if_copy_constructible<Container> other) : t(other.t) {}
  21.     Container(Container&& other) : t(std::move(other.t)) {}
  22. };
  23.  
  24. static_assert(std::is_copy_constructible<Container<int>>::value, "Non-Copyable");
  25. static_assert(!std::is_copy_constructible<Container<std::unique_ptr<int>>>::value, "Copyable");
  26.  
  27. Container<std::unique_ptr<int>> makeNonCopyableContainer() {
  28.     return Container<std::unique_ptr<int>>();
  29. }
  30.  
  31. int main () { 
  32.     Container<int> c1;
  33.     Container<int> c2(c1);
  34.     Container<std::unique_ptr<int>> c3;
  35.     // This would generate compile error:
  36.     // Container<std::unique_ptr<int>> c4(c3);
  37.     Container<std::unique_ptr<int>> c5(makeNonCopyableContainer());
  38.     return 0;
  39. }
Success #stdin #stdout 0s 3336KB
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https://ideone.com/B7TFmr
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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