I want to achieve some more complicated structure in fortran2008 and I am not sure how to do it according to the standard. So I am even not sure if it is a bug, or simply not possible with fortran2008. I want to make a base class, preferably an abstract one, which promises a subroutine which operates on TWO arguments of this base class. The derived class should implement this and there is some other class using this procedure which only knows about the base class. This was actually possible with gcc 4.7 by declaring both arguments of the subroutine as class. As an example, consider the following program (sorry, quite lengthy due to the several classes): module BaseModule implicit none private type, public, abstract :: BaseClass contains procedure(FuncAbstr), deferred :: Func end type abstract interface subroutine FuncAbstr(self, other) import class(BaseClass), intent(inout) :: self class(BaseClass), intent(in) :: other end subroutine end interface end module module UseBaseModule use BaseModule implicit none private type, public :: UseBaseClass class(BaseClass), pointer :: base => null() contains procedure :: Init procedure :: CallFunc end type contains subroutine Init(self, base) class(UseBaseClass), intent(inout) :: self class(BaseClass), pointer, intent(in) :: base self%base => base end subroutine subroutine CallFunc(self) class(UseBaseClass), intent(inout) :: self class(BaseClass), allocatable :: newBase allocate(newBase, mold=self%base) call newBase%Func(self%base) end subroutine end module module DerivedModule use BaseModule implicit none private type, public, extends(BaseClass) :: DerivedClass real :: x contains procedure :: Func end type contains subroutine Func(self, other) class(DerivedClass), intent(inout) :: self class(DerivedClass), intent(in) :: other self%x = other%x write(*,*) 'Derived Func called' end subroutine end module program Test use BaseModule use UseBaseModule use DerivedModule implicit none class(BaseClass), allocatable :: derived type(UseBaseClass) :: useBase allocate(DerivedClass :: derived) call useBase%Init(derived) call useBase%CallFunc() end program This code compiles and runs correctly with gcc4.7.3, but gcc4.8.2 gives the following compile error: Test1.f08:58.13: procedure :: Func 1 Error: Argument mismatch for the overriding procedure 'func' at (1): Type/rank mismatch in argument 'other' and some more which are not relevant. I actually do not even know if this code is supposed to compile, since it is not clear to me if such kind of overloading is allowed by the fortran standard. One way around this problem might be to give up the possibility to use an abstract type and to use a generic interface with an explicit type for the 2nd argument of the subroutine. The type is now required to facilite the resolution of the generic subroutine. However, this generic subroutine is not correctly resolved. As an example consider the following code (again quite lengthy, sorry): module BaseModule implicit none private type, public :: BaseClass contains procedure :: BaseFunc generic :: Func => BaseFunc end type contains subroutine BaseFunc(self, other) class(BaseClass), intent(inout) :: self type(BaseClass), intent(in) :: other write(*,*) 'Base Func called' end subroutine end module module DerivedModule use BaseModule implicit none private type, public, extends(BaseClass) :: DerivedClass real :: x contains procedure :: DerivedFunc generic :: Func => DerivedFunc !Extend generic Func end type contains subroutine DerivedFunc(self, other) class(DerivedClass), intent(inout) :: self type(DerivedClass), intent(in) :: other self%x = other%x write(*,*) 'Derived Func called' end subroutine end module module UseBaseModule use BaseModule implicit none private type, public :: UseBaseClass class(BaseClass), pointer :: base => null() contains procedure :: Init procedure :: CallFunc end type contains subroutine Init(self, base) class(UseBaseClass), intent(inout) :: self class(BaseClass), target, intent(in) :: base self%base => base end subroutine subroutine CallFunc(self) class(UseBaseClass), intent(in) :: self class(BaseClass), allocatable :: newBase allocate(newBase, mold=self%base) call newBase%Func(self%base) end subroutine end module program Test use DerivedModule use UseBaseModule implicit none type(DerivedClass) :: derived type(UseBaseClass) :: useBase call useBase%Init(derived) call useBase%CallFunc() end program This code compiles both with gcc4.7.3 and gcc4.8.2 and gives in both cases the incorrect output: Base Func called It should have called the DerivedFunc instead. Building a double block of select types around it solves the problem, but the UseBase needs to know about the Derived as well to do this, which is not desirable. Hope someone can help me out. Klaas Giesbertz
Sorry, the 2nd argument of Init of UseBase in the 1st test should have been target instead of pointer. In that case 'program Test' becomes the same as in the 2nd test.
(In reply to klaas_giesbertz from comment #0) > This code compiles and runs correctly with gcc4.7.3, but gcc4.8.2 gives the > following compile error: > > Test1.f08:58.13: > > procedure :: Func > 1 > Error: Argument mismatch for the overriding procedure 'func' at (1): > Type/rank mismatch in argument 'other' For your first example, I get this error with all version from 4.6 to trunk (with slight variations in the wording). Are you sure the code you posted is what you compiled with 4.7? > I actually do not even know if this code is supposed to compile, since it is > not clear to me if such kind of overloading is allowed by the fortran > standard. I think the error is correct. The Fortran standard does not allow this.
(In reply to klaas_giesbertz from comment #0) > This code compiles both with gcc4.7.3 and gcc4.8.2 and gives in both cases > the incorrect output: > Base Func called > It should have called the DerivedFunc instead. The second example is a bit tricky. Note that the resolution of your generic 'Func' happens at compile time and only based on the declared type -- the dynamic type of the objects does not matter at all. I would say the behavior here is ok as well.
In reply to Comment2&3 (Janus): I have copied it back from my post and it still compiles with my gfortran4.7.3. Could it have something to do with my build of gcc? I used macports to install it on my machine, so I am not fully aware of the dependencies. Would be strange though. Anyway, it is wrong fortran, so it should not work. A 'select type' could make the distinction, so 'select type' works dynamically, but the generic works statically. Confusing. So you would say that this kind of functionality is out of reach for fortran2008? Do you have any idea for a different solution? I know this is not the place to ask, but I would be grateful for some help.
(In reply to klaas_giesbertz from comment #4) > I have copied it back from my post and it still compiles with my > gfortran4.7.3. Could it have something to do with my build of gcc? Hopefully not, but it might have to do with the exact version. I just tried it with the most recent branch build: gcc version 4.7.4 20131219 (prerelease) [gcc-4_7-branch revision 206127] (GCC) (which yields the same result as the 4.7.3 version provided by Ubuntu, namely rejecting the test case). What does "gfortran -v" show in your case?
The test in comment 0 compiles with 4.7.3 and gives at run time Derived Func called And I confirm the reported behavior for the rest of the posts.
(In reply to Dominique d'Humieres from comment #6) > The test in comment 0 compiles with 4.7.3 and gives at run time Is this with the proper 4.7.3 release or some 4.7 branch build? Can you give the excact version (gfortran -v)? As mentioned in comment 5, it is being rejected with a current 4.7 branch build for me. Some commit on the 4.7 branch might have affected the behavior?
(In reply to janus from comment #7) > Some commit on the 4.7 > branch might have affected the behavior? After a quick look into the ChangeLog, I already have a suspicion: 2013-06-01 Janus Weil <janus@gcc.gnu.org> Tobias Burnus <burnus@net-b.de> PR fortran/57217 * interface.c (check_dummy_characteristics): Symmetrize type check.
When I say 4.7.3 it means the 4.7.3 release, otherwise I give the revision number or the date if the former is not available.
(In reply to Dominique d'Humieres from comment #9) > When I say 4.7.3 it means the 4.7.3 release, otherwise I give the revision > number or the date if the former is not available. Ok, that matches my suspicion (as that commit was after the 4.7.3 release).
Finally figured out how to make it work. I guess this is what the class(*) is useful for. Using class(*) I can simply overload Func and its resolution becomes dynamic. I consider the class(*) quite an overkill, but it works. So the Base and Derived Modules now become module BaseModule implicit none private type, public :: BaseClass contains procedure :: Func end type contains subroutine Func(self, other) class(BaseClass), intent(inout) :: self class(*), intent(in) :: other write(*,*) 'Base Func called' end subroutine end module module DerivedModule use BaseModule implicit none private type, public, extends(BaseClass) :: DerivedClass real :: x contains procedure :: Func end type contains subroutine Func(self, other) class(DerivedClass), intent(inout) :: self class(*), intent(in) :: other write(*,*) 'Derived Func called' select type(bla => other) class is (DerivedClass) write(*,*) 'DerivedClass found' class default write(*,*) 'Bad luck' end select end subroutine end module
(In reply to klaas_giesbertz from comment #11) > Finally figured out how to make it work. I guess this is what the class(*) > is useful for. Using class(*) I can simply overload Func and its resolution > becomes dynamic. I consider the class(*) quite an overkill, but it works. I don't think you need unlimited polymorphism, i.e. class(*), for what you're trying to do. It should be enough to declare the 'other' argument as 'class(BaseClass)' in both cases.
You are right! Thanks a lot.
In any case I will close this PR now, since I don't see any problems with gfortran's behavior on the test cases reported here.