(j3.2006) Would there be a technical problem if...

[Bill Long]

> On Jan 17, 2018, at 1:56 PM, Van Snyder <Van.Snyder at jpl.nasa.gov> wrote:
> 
> 
> Anyway, I still don't know whether there's a technical problem for the
> standard or for implementations to allow the passed-object argument to
> be an array.

I agree that none of the posts really addressed this. I?m not the expert on this stuff, but will try at least some comments. 

The passed-object dummy argument gets associated with the object that is the data-ref in the syntax

   call data-ref%binding-name

If the passed-object dummy is an array, then the data-ref would either need to be an array or broadcast to each element of the dummy.  Or the TBP needs to be elemental.  Interestingly in section on procedure reference, the data-ref in the call statement is allowed to be an array.  What that means in the case of the dummy being a scalar and the procedure not elemental is unclear.  I tried a naive example:

module modu

  type van
     integer :: i = 1
     procedure(van_tbp),pointer :: van_tbp
  contains
     procedure :: tbp => van_tbp
  end type van

contains

  subroutine van_tbp(pass_obj)
    class (van) :: pass_obj
    print *, "executed tbp", pass_obj%i
  end subroutine van_tbp

end module modu

program test
  use modu
  type(van) :: obj_ref, array_ref(10)

  print *, "call to obj_ref"
  call obj_ref%tbp
  print *, "call to array_ref"
  call array_ref(:)%tbp

end program test

With 4 compilers tried, 3 gave errors for mismatched ranks of the actual and dummy arguments.  The 4th accepted the code and printed output as if the dummy were a rank-1 array of size 10.  (The ?1? repeated 10 times.)  This is not too impossible considering that the dummy is declared CLASS and hence would be passed as a pointer to a descriptor. The descriptor contains enough information about rank, bounds, etc. to allow the code to run.   Malcolm or Tom can comment on the conformance of the code, but relying on this working is clearly not portable in practice. 

If the compiler allowed you to declared the passed-object argument as an array (constraint violation now), then the data-ref in the call could not be a scalar.  That sort of limitation might seem unacceptable to some. 

Cheers,
Bill


Bill Long                                                                       longb at cray.com
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