[Bug c++/63739] New: template id needed for constructor inheritance with using keyword

[darkdragon-001 at web dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63739

            Bug ID: 63739
           Summary: template id needed for constructor inheritance with
                    using keyword
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: darkdragon-001 at web dot de

There are problems with automatically determining the template id when
inheriting constructors with using keyboard.

In the following example there is only one case (out of four) which works as
expected (-> see NOTE comments)


#include <iostream>
#include <utility>

class A : public std::pair<int,bool> {
  // NOTE here it is not possible to ommit the template id
  // EXPECTED "using std::pair::pair;"
  using std::pair<int,bool>::pair;
};

template<class T>
class B : public std::pair<T,bool> {
  // NOTE here it is not possible to ommit the template id
  // EXPECTED "using std::pair::pair;"
  using std::pair<T,bool>::pair;
};

// NOTE following examples use namespace std
using namespace std;

class C : public pair<int,bool> {
  using pair::pair;
};

template<class T>
class D : public pair<T,bool> {
  // NOTE here it is not possible to ommit the template id
  // EXPECTED "using pair::pair;"
  using pair<T,bool>::pair;
};

int main() {
  A a(5,true);
  cout << "a.first:" << a.first << endl;

  B<int> b(5,true);
  cout << "b.first:" << b.first << endl;

  C c(5,true);
  cout << "c.first:" << c.first << endl;

  D<int> d(5,true);
  cout << "d.first:" << d.first << endl;

  return 0;
}