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  1. #include <iostream>
  2. #include <typeinfo>
  3. using namespace std;
  4. class Class {
  5. };
  6.  
  7. class Subclass : public Class {
  8. };
  9.  
  10. template<typename T>
  11. class Template1 {
  12. public:
  13. };
  14.  
  15. template<typename T>
  16. class Template2 {
  17. public:
  18.     template<typename Y>
  19.     Template2(Template1<Y>& t1)   // requires reference
  20.     {
  21.     	cout<<"Constructor conversion from reference to "<<typeid(t1).name()<<" to "<<typeid(*this).name()<<endl;
  22.     }
  23.     template<typename Y>
  24.     Template2(Template1<Y>&& t1)  // uses an rvalue reference (for temp)
  25.     // Template2(const Template1<Y>& t1)  // works also but assumes t1 is not changed
  26.     {
  27.     	cout<<"Constructor conversion from rvalue ref "<<typeid(t1).name()<<" to "<<typeid(*this).name()<<endl;
  28.     }
  29. };
  30.  
  31. Template2<Class> f1(Template2<Class>&& t2) {
  32.     cout<<"f1() will return: ";
  33.     return Template1<Subclass>();
  34. }
  35.  
  36. Template2<Class> f2(Template2<Class> t2) {
  37.     cout<<"f2() will return: ";
  38.     return Template1<Subclass>();
  39. }
  40.  
  41. int main() {
  42. 	cout<<"test1"<<endl;
  43.     f1(Template1<Subclass>()); // error C2664: 'Template2<Class> f1(Template2<Class> &)': cannot convert argument 1 from 'Template1<Subclass>' to 'Template2<Class> &'
  44. 	cout<<endl<<"test2"<<endl;
  45.     f2(Template1<Subclass>()); // OK
  46. 	cout<<endl<<"test3"<<endl;
  47.     f1(Template2<Class>(Template1<Subclass>())); // OK
  48. }
Success #stdin #stdout 0s 15240KB
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Standard input is empty
stdout
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test1
Constructor conversion from rvalue ref 9Template1I8SubclassE to 9Template2I5ClassE
f1() will return: Constructor conversion from rvalue ref 9Template1I8SubclassE to 9Template2I5ClassE

test2
Constructor conversion from rvalue ref 9Template1I8SubclassE to 9Template2I5ClassE
f2() will return: Constructor conversion from rvalue ref 9Template1I8SubclassE to 9Template2I5ClassE

test3
Constructor conversion from rvalue ref 9Template1I8SubclassE to 9Template2I5ClassE
f1() will return: Constructor conversion from rvalue ref 9Template1I8SubclassE to 9Template2I5ClassE
https://ideone.com/v52pip
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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