User defined type as argument to elemental subroutine?

Question

In my code I have an elemental subroutine which is basically like this:

elemental subroutine calc_stuff (x, a, b, c)
   real, intent(in)  :: a, b, c
   real, intent(out) :: x

   x = a/b + c

end subroutine calc_stuff

which I changed to this:

elemental subroutine calc_stuff (x, a, t)
   real,         intent(in)  :: a
   type(mytype), intent(in)  :: t
   real,         intent(out) :: x

   x = a/t%b + t%c

end subroutine calc_stuff

where mytype is a type containing some scalar real and integer, as well as a real, allocatable array. The members b and c are reals, making the second version basically the same as the first one.

The second version compiles fine on various compilers (Cray, Intel, NEC, GFortran), but now I read that the standard states for elemental subroutines:

All dummy arguments must be scalar, and must not have the ALLOCATABLE or POINTER attribute.

Is my code therefore not standard-conforming when passing a user-defined type to an elemental subroutine, but all the compilers "know" what I want because I am only using scalars from the type and not the allocatable array? Or am I misunderstanding the wording of the standard and everything is fine with the second version?

francescalus francescalus · Accepted Answer · 2018-07-11T06:47:25

The dummy argument t is scalar¹ and does not have the pointer attribute and does not have the allocatable attribute. It does not violate the condition.

The attributes of components of the type do not have a bearing on the attributes of the type itself.

¹ Being of derived type doesn't make an object necessarily non-scalar. Even with multiple, or array components, the object itself may still be scalar. A derived type array is an array with element(s) of that type. Think also of a character object like character(len=3) name: it is scalar but consists of multiple substrings.

User defined type as argument to elemental subroutine?

1 Answers