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  1. #include <iostream>
  2. #include <string>
  3. #include <vector>
  4. #include <cassert>
  5. using namespace std;
  6.  
  7. struct A {
  8.   A(int &&) { cout << "create A" << endl; }
  9.   A(A&&) { cout << "move A" << endl; }
  10.   ~A(){ cout << "kill A" << endl; }
  11. };
  12.  
  13. template <class T> struct B {
  14.   T value;
  15.   B() : value() { cout << "new B" << endl; }
  16.   B(const T &__a) : value(__a) { cout << "create B" << endl; }
  17.   B(const B &p) = default;
  18.   B(B && o) = default;
  19.   ~B(){ cout << "kill B" << endl; }; 
  20.   template <class U, class = typename enable_if<is_convertible<U, T>::value>::type>
  21.     B(U &&v) : value(std::forward<U>(v)) { 
  22.       cout << "new forward initialized B" << endl; 
  23.     }
  24. };
  25.  
  26. void foo(B<const A&> a){  cout << "Using A" << endl; }
  27.  
  28. template<typename T>
  29. void baz(const vector<B<T>> &test){
  30.   cout << "In Baz: " << endl; 
  31.   for(const auto &e : test) std::cout << e.value << endl;
  32. }
  33.  
  34. int main(){
  35.   cout << "Foo test case:" << endl;
  36.   foo( {123} );
  37.  
  38.   cout << "\nThis works as expexted::" << endl;
  39.   foo( A(123) );
  40.  
  41.   // passing strings around works
  42.   cout << "\nString test case:" << endl;
  43.   baz<std::string>({"Hello", "World"});
  44.  
  45.   // passing const reference doesn't
  46.   cout << "\nSecond string test case:" << endl;
  47.   baz<const std::string &>({"Hello", "World"});
  48. }
  49.  
Runtime error #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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Foo test case:
create A
new forward initialized B
kill A
Using A
kill B

This works as expexted::
create A
new forward initialized B
Using A
kill B
kill A

String test case:
new forward initialized B
new forward initialized B
In Baz: 
Hello
World
kill B
kill B
kill B
kill B

Second string test case:
new forward initialized B
new forward initialized B
In Baz:
https://ideone.com/BZ6tm4
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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