IV99402: TEMPLATE CONSTRUCTOR CONST PARAMETER NOT MATCHING

XL C/C++ for AIX Fix Pack 20 (March 2018 Update) for 12.1
XL C/C++ for AIX Fix Pack 21 (January 2019 Update) for 12.1

APAR status

• Closed as program error.

Error description

• After passing a complex typedef to a function that instantiates
  a template class, the template class has trouble determining the
  correct constructor to use.  The constructors are identical
  except for a const on the first parameter:
  
      TroubleType(U& u, typename Test<U, T>::type = 0)
      TroubleType(const U& u, typename Test<U, T>::type = 0)
  
  The compiler states that there is no best match.
  
  
  
     === TEST CASE ===
  
  template <class T, class U>
  struct Test {
      typedef void * type;
  };
  
  struct A {};
  
  template <int (*)(A *)>
  struct B {};
  
  template <class T>
  struct C {
      static int f(T *) { return 0; }
  };
  
  template <class FUNC>
  class Function {};
  
  int result = 12345;
  
  template <class T>
  struct TroubleType {
      template <class U>
      TroubleType(U& u, typename Test<U, T>::type = 0)
      {
          result = -99;
      }
  
      template <class U>
      TroubleType(const U& u, typename Test<U, T>::type = 0)
      {
          result = 0;
      }
  };
  
  typedef Function<void (*)(B<&C<A>::f> *)> F;
  
  void l(const F& f)
  {
      TroubleType<F> p( f);
  }
  
  int main()
  {
      F f;
      l(f);
      return result;
  }
  
  
  $ xlC_r -c apar.cpp
  "apar.cpp", line 40.20: 1540-0219 (S) The call to
  "TroubleType<Function<void (*)(B<&C<A>::f> *)>
  >::TroubleType<Function<void (*)(B<&C<A>::f> *)> >" has no best
  match.
  "apar.cpp", line 40.23: 1540-1228 (I) Argument number
  1 is an lvalue of type "const Function<void (*)(B<&C<A>::f>
  *)>".
  "apar.cpp", line 30.5: 1540-1202 (I) No candidate is
  better than "TroubleType<Function<void (*)(B<&C<A>::f> *)>
  >::TroubleType(const Function<void (*)(B<&C<A>::f> *)> &,
  type)".
  "apar.cpp", line 40.23: 1540-1231 (I) The conversion
  from argument number 1 to "const Function<void (*)(B<&C<A>::f>
  *)> &" uses "the identity conversion".
  "apar.cpp", line 24.5: 1540-1202 (I) No candidate is
  better than "TroubleType<Function<void (*)(B<&C<A>::f> *)>
  >::TroubleType(const Function<void (*)(B<&C<A>::f> *)> &,
  type)".
  "apar.cpp", line 40.23: 1540-1231 (I) The conversion
  from argument number 1 to "const Function<void (*)(B<&C<A>::f>
  *)> &" uses "the identity conversion".
  $
  

Local fix

• Remove const version of constructor.
  

Problem summary

• PROBLEM DESCRIPTION:
  An error during partial ordering caused invalid compiler errors
  (containing no file/line info) to be emitted.
  
  USERS AFFECTED:
  Users of overloaded function templates.
  

Problem conclusion

• The problem has been resolved.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  IJ04507 IJ08180

Fix information

• Fixed component name

  XL C/C++ FOR AI

• Fixed component ID

  5725C7200

Applicable component levels

• RC10 PSY

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