To: J3                                                     J3/19-250
From: John Reid & Reuben D. Budiardja & Daniel Chen
Subject: US 12, arrays of coarrays
Date: 2019-October-16

Discussion
----------

This paper proposes specs, syntax, and edits for US-12, see 18-280r1.

Proposed formal specifications
------------------------------

1. Allow an object of a derived type that has a coarray
ultimate component to be an array. There is a separate coarray for
each element of the parent array and coarrays in separate elements
are not required to have the same bounds and cobounds.

2. Allow an object of a derived type that has a coarray
ultimate component to be allocatable, which implies that it is also
allowed to be polymorphic.

3. In an allocate or deallocate statement for a coarray that is an
ultimate component of a polymorphic variable, the variable shall
have the same set of coarray components.

4. In an intrinsic assignment for a variable that has a coarray
ultimate component, <exp> and <var> must have the same type, the same
type parameters, and the same shape.


Proposed syntax
---------------

No new syntax.


Edits to 18-007r1
-----------------

[xiii] Introduction
Add
"A data object that has a coarray component is no longer restricted to
be scalar."
"A data object that has a coarray component is allowed to be allocatable."

[95:26-27] In 8.5.6 CODIMENSION attribute, change C825 to
"C825 An entity whose type has a coarray ultimate component shall
not be a pointer, shall not be a coarray, and shall not be a function
result."

[132:30] In 9.7.1.1 Form of the ALLOCATE statement, delete
"C937 (R927) type-spec shall not specify a type that has a coarray
ultimate component."

[134:17+] In 9.7.1.2 Execution of an ALLOCATE statement, at the end of
para 3, add
"When an ALLOCATE statement is executed for which an allocate-object is
a coarray, and if the coarray is an ultimate component of an array element,
it shall be the same element on all active images of the current team.

When an ALLOCATE statement is executed for which an allocate-object is
a coarray, and if the coarray is an ultimate component of a polymorphic
variable, the variable shall have the same set of coarray components."

[137:31] In 9.7.3.2 Deallocation of allocatable variables, para 10,
after the first sentence, add
"When a statement deallocates a coarray that is an ultimate component
of an array element, it shall be the same element on all active images
of the current team.

When a statement deallocates a coarray that is an ultimate component
of a polymorphic variable, the variable shall have the same set of
coarray components."

[160:1] In 10.2.1.2 Intrinsic assignment statement, para 1, item(1),
change "," to " or a data object with a coarray component," so that
the item becomes
"(1) if the variable is polymorphic it shall be allocatable and not a
coarray or a data object with a coarray component,"

[160:10] In 10.2.1.2 Intrinsic assignment statement, para 1, item(3),
change "not a coarray" to "not a coarray or an array of objects with
a coarray component" so that the item becomes
"(3) the variable and expr shall be conformable unless the variable
is an allocatable array that has the same rank as expr and is not
a coarray or an array of objects with a coarray component,"

[198:14] In 11.6.1 Image control statements, para 2, replace
bullet 5
  o ALLOCATE or DEALLOCATE statement that has a coarray allocate-object
by the two bullets
  o ALLOCATE statement that has a coarray allocation;
  o DEALLOCATE statement that has a coarray allocate-object or
    an allocate-object that has a coarray ultimate component;

[308:25-26] In 15.5.2.8 Coarray dummy variables, para 2, add
", is an array that has the CONTIGUOUS attribute and has
a coarray ultimate component," after "CONTIGUOUS attribute"
and change "is not of assumed shape" to "is neither of assumed
shape nor of assumed rank".
This makes the para. become
"If the dummy argument is an array coarray that has the CONTIGUOUS
attribute, is an array that has the CONTIGUOUS attribute and has
a coarray ultimate component, or is neither of assumed shape nor
of assumed rank, the corresponding actual argument shall be simply
contiguous or an element of a simply contiguous array."