error.txt

main.cpp:6:10: error: no viable conversion from 'A<Bar>' to 'A<Foo>'
  A<Foo> a = A<Bar>();
         ^   ~~~~~~~~
main.cpp:3:29: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from 'A<Bar>' to 'const A<Foo> &' for 1st argument
template <typename T> class A {};
                            ^
main.cpp:3:29: note: candidate constructor (the implicit move constructor) not viable: no known conversion from 'A<Bar>' to 'A<Foo> &&' for 1st argument
template <typename T> class A {};
                            ^
1 error generated.
make: *** [all] Error 1

main.cpp

class Foo {};
class Bar : public Foo {};
template <typename T> class A {};

int main() {
  A<Foo> a = A<Bar>();
  return 0;
}