Module procedures and abstract interfaces

Help
7

@rgaelzer ,

So, as discussed at comp.lang.fortran, you can investigate if the shown approach (repeated below for any reader’s sake who may not want to peruse another forum) is acceptable to you as a workaround that is kosher with the current standard. As you brought up, you can employ some “guards” by applying suitably the PUBLIC/PRIVATE attributes and even the PROTECTED one.

module implementations_m
contains
   function fun1(x,y) result(z)
      integer, intent(in) :: x
      integer, intent(in) :: y
      integer :: z
      z = x + y
   end function 
   function fun2(x,y) result(z)
      integer, intent(in) :: x
      integer, intent(in) :: y
      integer :: z
      z = 2*x + 3*y
   end function 
   function fun3(x,y) result(z)
      integer, intent(in) :: x
      integer, intent(in) :: y
      integer :: z
      z = x - y
   end function 
end module 
module m
   use implementations_m
   private
   abstract interface
      function Ifun(x,y) result(z)
         integer, intent(in) :: x
         integer, intent(in) :: y
         integer :: z
      end function 
   end interface
   procedure(Ifun), protected, pointer, public :: fun => null() ! or set to default
   public :: setfun
contains
   subroutine setfun( fun_name )
      character(len=*), intent(in) :: fun_name
      select case ( fun_name )
         case ( "fun1" )
            fun => fun1
         case ( "fun2" )
            fun => fun2
         case ( "fun3" )
            fun => fun3
         case default 
            ! error stop?
      end select
   end subroutine 
end module
   use m
   call setfun( "fun2" )
   print *, fun(3, 4) 
end

C:\Temp>ifort /standard-semantics p.f90
Intel(R) Fortran Intel(R) 64 Compiler Classic for applications running on Intel(R) 64, Version 2021.3.0 Build 20210609_000000
Copyright (C) 1985-2021 Intel Corporation. All rights reserved.

Microsoft (R) Incremental Linker Version 14.29.30038.1
Copyright (C) Microsoft Corporation. All rights reserved.

-out:p.exe
-subsystem:console
p.obj

C:\Temp>p.exe
18

You still have considerable verbosity unfortunately. Additionally you have the work toward a setter method and the instructions therein. Then there is the run-time invocation of setfun. But the gain will be your consumer (who may be you yourself but often with different incarnations and memory recall in the future!) can mimic a generic interface in the use of the method i.e., if that is of any value.