To: J3                                                     J3/22-175
From: John Reid
Subject: Remote polymorphic subobjects
Date: 2022-July-19
References: 22-007r1

Discussion
----------

Existing constraints suggest an implementation would never need to
query the dynamic type of an object on another image.

R911 is

"R911 data-ref is part-ref [ % part-ref ] ..."

C917 states

C917 (R911) Except as an actual argument to an intrinsic inquiry
      function or as the designator in a type parameter inquiry, a
	  data-ref shall not be a coindexed object that has a polymorphic
	  allocatable potential  subobject component."

and C1528 states

C1528 (R1522) A data-ref shall not be a polymorphic subobject of a
       coindexed object.

C918 says

C918 Except as an actual argument to an intrinsic inquiry function or as
     the designator in a type parameter inquiry, if the rightmost
	 part-ref is polymorphic, no other part-ref shall be coindexed.

The list of intrinsic inquiry functions includes SAME_TYPE_AS and
EXTENDS_TYPE_OF, so those intrinsics should be excluded in constraints
C917 and C918 to avoid a requirement of knowing the dynamic type on a
remote image.


Edits to 22-007r1:

[133:13, 9.4.2 Structure components, Constraint C917] After "intrinsic
inquiry function", add "other than SAME_TYPE_AS, EXTENDS_TYPE_OF, ",
leading to the whole constraint reading "Except as an actual argument
to an intrinsic inquiry function other than SAME_TYPE_AS, EXTENDS_TYPE_OF,
or as the designator in a type parameter inquiry, a data-ref shall not
be a coindexed object that has a polymorphic allocatable potential
subobject component."

[133:16, 9.4.2 Structure components, Constraint C918] After "intrinsic
inquiry function", add "other than SAME_TYPE_AS, EXTENDS_TYPE_OF, "
leading to the whole constraint reading "Except as an actual argument
to an intrinsic inquiry function other than SAME_TYPE_AS, or
EXTENDS_TYPE_OF, or as the designator in a type parameter inquiry, if
the rightmost part-ref is polymorphic, no other part-ref shall be
coindexed.