Fortran generic functions based on the return kind

Question

I am trying to create a generic function in Fortran based on the value to be returned, that is, depending on if the output of the function is to be assigned to a single prec

Answer 1

Following the advice by Vladimir F, I had a look at the transfer intrisic function and added a mold parameter to my functions to set the return type.

If any input argument to the functions were real they could be used to set the return type as High Performace Mark stated, but since this is not my case I finally used the mold variable.

Now it compiles and work. The code is:

MODULE kk_M

   USE ISO_FORTRAN_ENV

   IMPLICIT NONE

   INTEGER, PARAMETER :: sp = REAL32
   INTEGER, PARAMETER :: dp = REAL64

   INTERFACE use_func
      MODULE PROCEDURE use_sp_func
      MODULE PROCEDURE use_dp_func
   END INTERFACE use_func

   INTERFACE use_sub
      MODULE PROCEDURE use_sp_sub
      MODULE PROCEDURE use_dp_sub
   END INTERFACE use_sub

   CONTAINS

   FUNCTION use_sp_func(mold) RESULT(res)
      REAL(KIND=sp),INTENT(IN) :: mold
      REAL(KIND=sp) :: res
      IF (.FALSE.) res = mold !To avoid compilation warning about unused variable
      res = 5._sp
   END FUNCTION use_sp_func

   FUNCTION use_dp_func(mold) RESULT(res)
      REAL(KIND=dp),INTENT(IN) :: mold
      REAL(KIND=dp) :: res
      IF (.FALSE.) res = mold !To avoid compilation warning about unused variable
      res = 5._dp
   END FUNCTION use_dp_func

   SUBROUTINE use_sp_sub(res)
      REAL(KIND=sp), INTENT(OUT) :: res
      res = 5._sp
   END SUBROUTINE use_sp_sub

   SUBROUTINE use_dp_sub(res)
      REAL(KIND=dp), INTENT(OUT) :: res
      res = 5._dp
   END SUBROUTINE use_dp_sub

END MODULE kk_M


PROGRAM kk
   USE kk_M
   IMPLICIT NONE
   REAL(KIND=sp) :: num_sp
   REAL(KIND=dp) :: num_dp

   num_sp = use_func(1._sp)
   WRITE(*,*) num_sp

   num_dp = use_func(1._dp)
   WRITE(*,*) num_dp

   CALL use_sub(num_sp)
   WRITE(*,*) num_sp

   CALL use_sub(num_dp)
   WRITE(*,*) num_dp

END PROGRAM kk