f2003/f2008, class/extends, multiple gemeric assignment

[Paul Kapinos]

Dear Fortran gurus,
please take a look at the attached example. It cannot be compiled using the 
gfortran/4.8.1:

 > $ gfortran -c ___MOD_paul.f90
 > ___MOD_paul.f90:42.42:
 >
 >     generic            :: assignment(=) => assign2
 >                                           1
 > Error: 'ass_gf' and 'ass_en' for GENERIC '=' at (1) are ambiguous

Actually this code piece is derived from an real world code which is developed 
using Intel compiler (may be compiled with ifort, runs OK) and the actual 
prevents from porting the code (being still in development) to 'gfortran'.

Well, let's take a look at the code.
- module 'kleiner' is no problem - can be compiled when in own file. Type 
'mytype' is defined and '=' is bound to this type.
- module 'grosser' is meant to be a subclass of 'kleiner': the type 'zwotype' 
extends the type 'mytype'. Again '=' should be bound to the new (derived) type 
'zwotype' - and this fals.

Well, as said the Intel's "ifort" compile this with no warnings and AFAIK the 
code also runs well. The question now is:
- is that some Intel's extension, or
- is that an Fortran 2003/2008 feature still not supported in gfortran, or
- is the code in any way not Fortran-standard complying?

It would be quite vital for our user to know what is the root of the evil in 
order to decide what to do with the code now. (as said the example is derived 
from a bigger an fairly complicated code).

Best from Aachen

Paul Kapinos

P.S. Note that 'ass_gf' and 'ass_en' have *different* signatures:

 > subroutine ass_en(result,incoming)
 > class (mytype), intent (out) :: result
 > class (*), intent (in)          :: incoming

 > subroutine ass_gf(result,incoming)
 > class (zwotype), intent (out) :: result
 > class (*), intent (in)        :: incoming

whereby, yes, 'zwotype' is derived from (but not equal to!) 'mytype'

-- 
Dipl.-Inform. Paul Kapinos   -   High Performance Computing,
RWTH Aachen University, Center for Computing and Communication
Seffenter Weg 23,  D 52074  Aachen (Germany)
Tel: +49 241/80-24915
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module kleiner
implicit none

type mytype
  real,private   :: meane              = 0.0
contains
  generic, public            :: assignment(=) => assign
  procedure, private         :: assign        => ass_en
end type mytype

contains

subroutine ass_en(result,incoming)
implicit none

 class (mytype), intent (out) :: result
 class (*), intent (in)          :: incoming

 select type (incoming)
  type is (mytype)
     result%meane    = 1.0
  type is (real)
     result%meane    = incoming
  class default
    write(*,*) 'Type mismatch in type mytype'; stop
 end select
end subroutine ass_en

end module kleiner

!------------------------------------------------------------------------------!


module grosser

use kleiner, only: mytype
implicit none

type, extends(mytype) :: zwotype
    real,private   :: flux_
  contains
    generic            :: assignment(=) => assign2
    procedure, private :: assign2 => ass_gf
end type zwotype

contains

subroutine ass_gf(result,incoming)
implicit none

 class (zwotype), intent (out) :: result
 class (*), intent (in)        :: incoming

select type (incoming)
  type is (mytype)
  type is (zwotype)
      result%flux_              = 42.0
  type is (real)
  class default
    write(*,*) 'Type mismatch in type zwotype'
    stop
end select
end subroutine ass_gf

end module grosser
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