class - Template in Fortran?

Question

I have a module that defines three types and and some operations on them.

In a separate module, I want to define an algorithm that operates on either one of these types using the operations defined in the module. The algorithm is the same, regardless of the type. I can overload it, but I was wondering if I can save a lot of typing by defining some sort of template algorithm. What I have in mind is something like class templates in C++.

Thanks

Answer 1

Fortran does not have templates, but you can put the code common to the functions handling different types in an include file as a kludge to simulate templates, as shown in this code:

! file "cumul.inc"
! function cumul(xx) result(yy)
! return in yy(:) the cumulative sum of xx(:)
! type, intent(in) :: xx(:)
! type             :: yy(size(xx))
integer :: i,n
yy = 0
n  = size(xx)
if (n < 1) return
yy(1) = xx(1)
do i=2,n
   yy(i) = yy(i-1) + xx(i)
end do
return
! end function cumul
! end file "cumul.inc"

module foo
implicit none
integer, parameter :: sp = kind(1.0), dp = kind(1.0d0)
interface cumul
   module procedure cumul_double,cumul_real,cumul_int
end interface cumul
contains
!
function cumul_double(xx) result(yy)
real(kind=dp), intent(in) :: xx(:)
real(kind=dp)             :: yy(size(xx))
include "cumul.inc"
end function cumul_double
!
function cumul_real(xx) result(yy)
real(kind=sp), intent(in) :: xx(:)
real(kind=sp)             :: yy(size(xx))
include "cumul.inc"
end function cumul_real
!
function cumul_int(xx) result(yy)
integer, intent(in) :: xx(:)
integer             :: yy(size(xx))
include "cumul.inc"
end function cumul_int
end module foo

program xcumul
use foo, only: cumul
print*,cumul([10,20,30])
print*,cumul(sin([10.0,20.0,30.0]))
print*,cumul(sin([10.0d0,20.0d0,30.0d0]))
end program xcumul
! output:
! 10 30 60
! -0.5440211 0.36892414 -0.6191075
! -0.5440211108893698 0.3689241398382579 -0.6191074842546039

The tool mentioned in the paper

Car, David and Michael List (2010). PyF95++: A Templating Capability for the Fortran 95/2003 Language. ACM Fortran Forum 29(1), 2-20.

may interest you. I have not tried it.