(j3.2006) (SC22WG5.3665) [ukfortran] N1755: Request for new features from MPI Forum

[Van Snyder]

On Tue, 2008-11-11 at 15:51 -0800, Bill Long wrote:

> > 2. "C559 An entity with the VOLATILE attribute shall be a variable that is not
> > an INTENT (IN) dummy argument."
> > Please explain this one to me.
> >
> 
> INTENT(IN) implies that the dummy argument does not change its value
> (for the non-pointer case) inside the subprogram.  It allows the
> compiler to snap a copy of the variable in a register and keep it there
> throughout execution of the subprogram, for example.  Pretty much
> completely incompatible with the implications of volatile.

Mo, INTENT(IN) says that such a dummy argument shall not appear in a
variable definition context.  Without VOLATILE that's (almost) the same
thing, but if the actual argument really is volatile, wouldn't
INTENT(IN) + VOLATILE say "don't take a copy?"

Given that INTENT(IN) on its own is incompatible with VOLATILE, isn't
that a reason to specify VOLATILE when it's needed, instead of not being
able to specify it?

Prohibiting VOLATILE + VALUE is even more nonsensical, since the
procedure is allowed to change VALUE dummy arguments.  Why can't one
change while you're not looking?  VOLATILE + VALUE means "take a copy,
and then the copy might change while you're not looking."

Do we prohibit these?

  integer, intent(in), target :: X
  integer, pointer, volatile :: Y
  Y => X
  call foobar ( Y ) ! which keeps Y and makes volatile changes
                    ! to its target

  integer, value, target :: X
  integer, pointer, volatile :: Y
  Y => X
  call foobar ( Y ) ! which keeps Y and makes volatile changes
                    ! to its target

I couldn't find a constraint in 7.2.2 "If the <pointer-object> has the
VOLATILE attribute the target shall not have the VALUE or INTENT(IN)
attributes."

If we don't prohibit them, why bother with the cases that don't involve
pointers?

I also didn't find constraints in 5.3.18-19 against TARGET + VALUE or
VOLATILE.

Indeed, I didn't find a constraint against TARGET + INTENT(IN), so I
hope INTENT(IN) doesn't mean what Bill says, at least in this case.

-- 
Van Snyder                    |  What fraction of Americans believe 
Van.Snyder at jpl.nasa.gov       |  Wrestling is real and NASA is fake?
Any alleged opinions are my own and have not been approved or
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