Re: [orbitcpp-list] warnings

[Laszlo M. <las...@et...>]

> I need to do some work in this area. Any info on what sort of hacks
> mico and omniorb use (or where to look for them) would be very
> helpful.

OK, mico does this in include/var.h:

template<class T>
class ObjVar
{
  // [...]
// g++ const overload problem
#ifdef HAVE_CONST_OVERLOAD
  operator T*() const
  {
      return _ptr;
  }
  operator T*&()
  {
      check();
      return _ptr;
  }
#else
  operator T*&() const
  {
      ((ObjVar<T>*)this)->check();
      return (T*&)_ptr;
  }
#endif
}

and here is the test from its aclocal.m4

AC_DEFUN(AC_CONST_OVERLOAD,
[AC_MSG_CHECKING(for const overload)
AC_CACHE_VAL(ac_cv_have_const_overload,
[ac_cv_tmp_old_cxxflags="$CXXFLAGS"
if test X"$GXX" = Xyes; then
  CXXFLAGS="-Werror $CXXFLAGS"
fi
AC_TRY_COMPILE_GLOBAL(,[
  struct S {
    int *i;
    operator const int *() const { return i; }
    operator int *&() { return i; }
    operator const int &() const { return *i; }
    operator int &() { return *i; }
  };

  void bar (const int &, int &, const int *, int *, int *&);

  void foo (S &s, const S &cs)
  {
     int i = s; i = cs; i = *s; i = *cs;
     bar (s, s, s, s, s);
     bar (cs, s, cs, s, s);
  }
],
eval "ac_cv_have_const_overload=yes",
eval "ac_cv_have_const_overload=no",)
CXXFLAGS=$ac_cv_tmp_old_cxxflags
])


>  >    operator Base&()
>  > So I guess, this code could be safely removed.
> Hmmm - I suspect not. The thing is that we aren't using real C++
> objects, we're casting ORBit C objects into C++ ones, and using these
> cast operators to insure that the compiler doesn't try to do smart
> thunking in the case of multiple inheritance downcasts.  This provides
> a good speed increase over wrapping the C objects in C++ ones.

The problem is that as the warning says, gcc will NOT USE that operator
when it does the casting. Consider this example:

struct Base
{};

Base dummy;

struct Derived  : public Base
{
    operator Base &() { return dummy; }
};

gcc gives:
x.cc:8: warning: conversion to a reference to a base class will never
use a type conversion operator

And gcc is right, because it's totally silly what I'm doing.
I have no idea, why this is only a warning, IMHO it should be an error.

> Does the 'everything' test in orbitcpp CVS work with gcc 2.96?

Well, I just checked whether this const/non const warning is still
there, and didn't compile anything useful (I doubt I could - 2.96
is not binary compatible with my libraries).

Laszlo