Typesafe aliases of primitives with zero runtime overhead

safety.f90

module indices
  type :: localIdx
    integer :: val
  end type localIdx

  type :: globalIdx
    integer :: val
  end type globalIdx

contains

  function local2global(local) result(global)
    type(localIdx), intent(in) :: local
    type(globalIdx) :: global

    global%val = 2*local%val
  end function local2global

  function global2local(global) result(local)
    type(globalIdx), intent(in) :: global
    type(localIdx) :: local

    local%val = global%val/2
  end function global2local

end module indices 

program test
  use indices
  implicit none
  
  type(localIdx) :: loc
  type(globalIdx) :: glob

  loc%val = 8

  glob = local2global(loc) ! Valid function application

  glob = local2global(glob) ! Error: Type mismatch in argument 'local' at (1); passed TYPE(globalidx) to TYPE(localidx)
  glob = local2global(8) ! Error: Type mismatch in argument 'local' at (1); passed INTEGER(4) to TYPE(localidx)

  write(*,*) loc%val, glob%val

contains

end program safety