[WIP] Starting work on static members

[aprokop]

So far, the wrapper and proxy codes are generated. The remaining issue is: what is the proper access model to those functions in Fortran? I'm not sure, does Fortran have a concept of static member variables/functions?

[aprokop]

It seems like there is a nopass attribute. Is that what I should use?

[aprokop]

In case you missed the thread, @sethrj @youngmit

[aprokop]

Assuming i is a static member variable, would the proper .f90 be something like this:

! This file was automatically generated by SWIG (http://www.swig.org).
! Version 3.0.12
!
! Do not make changes to this file unless you know what you are doing--modify
! the SWIG interface file instead.
module static_members
 use, intrinsic :: ISO_C_BINDING
 implicit none

 ! PUBLIC METHODS AND TYPES
 public :: BaseClass
 ! TYPES
 type :: BaseClass
  type(C_PTR), private :: ptr = C_NULL_PTR
  logical, private :: own = .false.
 contains
  procedure :: create => swigf_new_BaseClass
  procedure :: release => swigf_delete_BaseClass
  procedure, nopass :: get_i => swigf_get_BaseClass_i
  procedure, nopass :: set_i => swigf_set_BaseClass_i
 end type

 ! WRAPPER DECLARATIONS
 private
 interface
  subroutine swigc_set_BaseClass_i(farg1) &
     bind(C, name="swigc_set_BaseClass_i")
   use, intrinsic :: ISO_C_BINDING
   integer(C_INT), intent(in) :: farg1
  end subroutine
  function swigc_get_BaseClass_i() &
     bind(C, name="swigc_get_BaseClass_i") &
     result(fresult)
   use, intrinsic :: ISO_C_BINDING
   integer(C_INT) :: fresult
  end function
  function swigc_new_BaseClass() &
     bind(C, name="swigc_new_BaseClass") &
     result(fresult)
   use, intrinsic :: ISO_C_BINDING
   type(C_PTR) :: fresult
  end function
  subroutine swigc_delete_BaseClass(farg1) &
     bind(C, name="swigc_delete_BaseClass")
   use, intrinsic :: ISO_C_BINDING
   type(C_PTR), value :: farg1
  end subroutine
 end interface

contains
  ! FORTRAN PROXY CODE
  subroutine swigf_set_BaseClass_i(i)
   use, intrinsic :: ISO_C_BINDING
   integer(C_INT), intent(in) :: i
   call swigc_set_BaseClass_i(i)
  end subroutine
  function swigf_get_BaseClass_i() &
     result(fresult)
   use, intrinsic :: ISO_C_BINDING
   integer(C_INT) :: fresult
   fresult = swigc_get_BaseClass_i()
  end function
  subroutine swigf_new_BaseClass(self)
   use, intrinsic :: ISO_C_BINDING
   class(BaseClass) :: self
   if (c_associated(self%ptr)) call self%release()
   self%ptr = swigc_new_BaseClass()
   self%own = .true.
  end subroutine

 subroutine swigf_delete_BaseClass(self)
   use, intrinsic :: ISO_C_BINDING
   class(BaseClass) :: self
   if (self%own) then
    call swigc_delete_BaseClass(self%ptr)
    self%own = .false.
   end if
   self%ptr = C_NULL_PTR
  end subroutine
end module static_members

and the test be

#define ASSERT(conditional) \
if (.not. conditional) then; \
  stop 1; \
endif


program test_static
use static_members

class(BaseClass), pointer :: v1 => null()
class(BaseClass), pointer :: v2 => null()

! Set variables
call v1%create()
call v1%set_i(2)
ASSERT(v1%get_i() == 2)

call v2%create()
call v2%set_i(3)
ASSERT(v1%get_i() == 3)

call v1%release()
call v2%release()

deallocate(v1)
deallocate(v2)

end program

or something else?

[aprokop]

I've updated the PR. I think static variables and functions should work now.

[aprokop]

I should mention the way things are done now. For every static member variable, SWIG generates a C++ wrapper called something like swigc_set_ClassName_VariableName with a corresponding Fortran proxy code. In the Fortran class interface, I rename them to set_VariableName and get_VariableName. Potentially, this may lead to collision when the class already has a function with that name, as I believe it would be mapped to the same API.

I'm not going to worry about that for now. I think for Trilinos that is going to be a rare case, partly because of the CamelCase style of function names.

[wawiesel]

Seth asked me to weigh in here if I thought of anything to add. I am a long time Fortran user and know a fair bit of C++ as well. In C++ you can call a static either of these ways:

BaseClass::set_i(10); 
//or
BaseClass instance;
instance.set_i(10); 

but unfortunately OO Fortran doesn't really have the first concept. The NOPASS gives you the second, but for the first, you really just need to call the underlying function:

!Fortran equivalent of C++ BaseClass::set_i(10)
call BaseClass_set_i(10)

For this reason, you might want to make sure fortran-bound statics have good names and are public.