LI71532: TEMPLATE CLASS WITH SINGLE OPERATOR= GIVES NO BEST MATCH ERROR

Latest updates for XL C/C++ Advanced Edition V8 for Linux
May 2009 Updates for XL C/C++ Advanced Edition V8 for Linux

APAR status

• Closed as program error.

Error description

• Compiler claims 'The call to "operator=" has no best match.'
  when in fact there is only one operator= that matches the call.
  This happens in a simple case of a template class with a single
  operator= function.  The compiler seems to find a conflict
  between the operator= and itself.
  
  TESTCASE:
  ---------
  template <class _T>
  class C
  {
  public:
          C<_T>& operator= (_T* pt)
          {
                  return *this;
          }
          void fn() {
                  operator= (0);
          }
  };
  
  extern void f ()
  {
          C<int> c;
          c.fn();
  }
  
  Actual Output:
  --------------
  xlC t.C
  "t.C", line 10.17: 1540-0219 (S) The call to "operator=" has no
  best match.
  "t.C", line 10.17: 1540-1230 (I) Argument number 1 is the
  implicit "this" argument.
  "t.C", line 10.28: 1540-1229 (I) Argument number 2 is an rvalue
  of type "int".
  "t.C", line 5.16: 1540-1202 (I) No candidate is better than
  "C<int>::operator=(int *)".
  "t.C", line 10.17: 1540-1231 (I) The conversion from argument
  number 1 to "C<int> &" uses "the identity conversion".
  "t.C", line 10.28: 1540-1231 (I) The conversion from argument
  number 2 to "int *" uses "a pointer conversion".
  "t.C", line 5.16: 1540-1202 (I) No candidate is better than
  "C<int>::operator=(int *)".
  "t.C", line 10.17: 1540-1231 (I) The conversion from argument
  number 1 to "C<int> &" uses "the identity conversion".
  "t.C", line 10.28: 1540-1231 (I) The conversion from argument
  number 2 to "int *" uses "a pointer conversion".
  "t.C", line 9.14: 1540-0700 (I) The previous message was
  produced while processing "C<int>::fn()".
  "t.C", line 17.10: 1540-0700 (I) The previous message was
  produced while processing "f()".
  

Local fix

• use -qlanglvl=noDependentBaseLookup
  

Problem summary

• The presense of operator= in a template class sometimes led to
  a duplicate declaration in the list of overload candidates.
  The duplicate will cause overload resolution to fail
  complaining about 2 candidates that are actually the same
  

Problem conclusion

• The error has been fixed so that no duplicates appear in the
  list of candidates in this case. Please apply the PTF.
  

Temporary fix

Comments

APAR Information

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

  IY85336

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

Fix information

• Fixed component name

  XLC/C++ RHEL4

• Fixed component ID

  5724M1610

Applicable component levels

• R800 PSN

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