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template <typename T> struct item {
  operator item<const T> () const { return item<const T>(); }
};
 
void conversionToConstRefWorks (const item<const int> &) { }
 
template <typename T> 
void butNotWhenTemplated (const item<const T> &) { }
 
int main () {
 
  item<int> i;
  item<const int> ci;
 
  // these all compile fine:
  conversionToConstRefWorks(ci);
  conversionToConstRefWorks(i);
  butNotWhenTemplated(ci);
 
  // but this one fails:
  butNotWhenTemplated(i); 
 
}

prog.cpp: In function ‘int main()’:
prog.cpp:21:24: error: no matching function for call to ‘butNotWhenTemplated(item<int>&)’
   butNotWhenTemplated(i);
                        ^
prog.cpp:8:6: note: candidate: ‘template<class T> void butNotWhenTemplated(const item<const T>&)’
 void butNotWhenTemplated (const item<const T> &) { }
      ^~~~~~~~~~~~~~~~~~~
prog.cpp:8:6: note:   template argument deduction/substitution failed:
prog.cpp:21:24: note:   types ‘const T’ and ‘int’ have incompatible cv-qualifiers
   butNotWhenTemplated(i);
                        ^

Standard output is empty