Fortran procedure pointer to subroutines in derived type

Question

In Fortran, I need a procedure pointer inside a derived type that can point to one of several subroutines. This problem seems to be common on SO:

Fortran save proced

Answer 1

Here's my working example:

module obj_mod
    integer, parameter :: n = 5

    type obj_type
        procedure(sub_interface), pointer, nopass :: obj_sub => NULL()
    end type

    interface
        subroutine sub_interface(y, x)
            import n
            double precision, dimension(n) :: x, y
        end subroutine sub_interface
    end interface

contains 
    subroutine sq_sub(x, y)
        double precision, dimension(n) :: x, y
        y = x ** 2
    end subroutine

    subroutine exp_sub(x, y)
        double precision, dimension(n) :: x, y
        y = exp(x)
    end subroutine

end module 

program member_subroutine
    use obj_mod
    type(obj_type) obj
    double precision, dimension(n) :: x, y

    x = (/ 1, 2, 3, 4, 5 /)
    write(*,*) 'x =', x

    obj%obj_sub => sq_sub
    call obj%obj_sub(x, y)
    write(*,*) 'y1 =', y

    obj%obj_sub => exp_sub
    call obj%obj_sub(x, y)
    write(*,*) 'y2 =', y
end program member_subroutine