[Bug fortran/64138] gfortran interface issue

["kargl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64138

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2014-12-01
     Ever confirmed|0                           |1

--- Comment #4 from kargl at gcc dot gnu.org ---
(In reply to kargl from comment #1)
> (In reply to david from comment #0)
> > Hi,
> > 
> >    I have created a complex number module:
> > 
> >        module complex_number_module
> >         implicit none
> > 
> >         integer, parameter :: loc_real_precision = 8
> > 
> >         type complex_number
> >           real(kind=loc_real_precision) :: real_part, imag_part
> >         end type complex_number
> > 
> >         interface c_sub
> >           module procedure c_sub_cc,    &      ! z1 - z2
> >                            c_sub_cr,    &      ! z1 - num, where num is a
> > real number
> >                            c_sub_rc            ! num - z1, where num is a
> > real number
> >         end interface
> > 
> > ! --------------------------------------------------------------------------
> >         type (complex_number) function c_sub_cc (z1, z2)
> > 
> >         type (complex_number), intent(in) :: z1, z2
> > 
> >         c_sub_cc%real_part = z1%real_part - z2%real_part
> >         c_sub_cc%imag_part = z1%imag_part - z2%imag_part
> > 
> >         end function c_sub_ccj
> > 
> > ! --------------------------------------------------------------------------
> >         type (complex_number) function c_sub_cr (z1, num)
> > 
> >         type (complex_number),     intent(in) :: z1
> >         real(kind=loc_real_precision), intent(in) :: num
> > 
> >         c_sub_cr%real_part = z1%real_part - num
> >         c_sub_cr%imag_part = z1%imag_part
> > 
> >         end function c_sub_cr
> > 
> > ! --------------------------------------------------------------------------
> >         type (complex_number) function c_sub_rc (num, z1)
> > 
> >         type (complex_number),     intent(in) :: z1
> >         real(kind=loc_real_precision), intent(in) :: num
> > 
> >         c_sub_rc%real_part = num - z1%real_part
> >         c_sub_rc%imag_part = - z1%imag_part
> > 
> >         end function c_sub_rc
> > 
> >       end module complex_number_module
> > 
> > When I compile with gfortran (version 4.6.4), I got the following error:
> > 
> > module_twoway_rrtmg_aero_optical_util.F:14.85:
> > 
> >                  c_sub_rc            ! num - z1, where num is a real number
> >                                                                            1
> > 
> > Error: Ambiguous interfaces 'c_sub_rc' and 'c_sub_cr' in generic interface
> > 'c_sub' at (1)
> > 
> > I don't see any ambiguity and I don't encounter any problem with other
> > compilers such pgi and ifort. Please advise.
> > 
> > Cheers,
> > David
> 
> Please attach the exact code you tried to compile.  The above is nonsense.

I fixed the above code.  I believe gfortran is correct to complain
about an ambiguous interface.  In the last two line below, which
of c_sub_rc and c_sub_cr should be called.

program foo
  use complex_number_module
  type(complex_number) a, b
  real(dp) x
  a%re = 1
  a%im = 2
  x = 1
  b = c_sub(a, x); print '(A,2F5.1)', 'a-x = ', b%re, b%im
  b = c_sub(x, a); print '(A,2F5.1)', 'x-a = ', b%re, b%im
  b = c_sub(z1=a, num=x); print '(A,2F5.1)', 'a-x = ', b%re, b%im
  b = c_sub(num=x,a); print '(A,2F5.1)', 'a-x = ', b%re, b%im
end program foo