[J3] Co-array question

[John Reid]

Malcolm Cohen via J3 wrote:
>
> Mark LeAir writes:
>
> And is the following in violation of any constraint, or is it now a 
> conforming program?
>
> program main
>
>   type :: type
>
>     integer, allocatable :: coarray[:]
>
>   end type
>
>   type(type), save, target :: object
>
>   class(*), pointer :: pointer
>
>   class(*), allocatable :: allocatable
>
>   allocate(object%coarray[*]);
>
>   pointer => object
>
>   allocate(allocatable, source = pointer)
>
> end
>
> John Reid opines:
>
> I think we have an omission here. I see no constraint that disallows it
> but it should not be allowed.
>
> My response:
>
> There is nothing here that warrants a constraint – the only 
> possibility would be to prohibit the pointer assignment: goodbye 
> bathwater, goodbye baby.
>
It is the allocate statement that is a problem, not the pointer assignment.
>
> The pointer can of course be used safely, viz contexts other than as 
> input to SOURCE=.
>
Agreed.
>
> The program is, I think, non-conforming because the standard does not 
> say what happens. For normal allocatable components there would be a 
> copy made, but that doesn’t apply to coarray components so “no 
> interpretation is established”.
>
> I agree that a requirement on the dynamic type of source-expr (in 
> F2018) that it not have a coarray ultimate component would appear to 
> be desirable. (In F202x, that probably should only apply to SOURCE=.)
>
In the context of F2018, it does not seem right that an allocation be 
allowed by referring to an object through a pointer but not by referring 
to the object directly.

John.
>
> Cheers,
>
> -- 
>
> ..............Malcolm Cohen, NAG Oxford/Tokyo.
>
> *From:* J3 <j3-bounces at mailman.j3-fortran.org> *On Behalf Of *Mark 
> LeAir via J3
> *Sent:* Thursday, August 19, 2021 2:01 AM
> *To:* fortran standards email list for J3 (j3 at mailman.j3-fortran.org) 
> <j3 at mailman.j3-fortran.org>
> *Cc:* Mark LeAir <mleair at nvidia.com>
> *Subject:* [J3] Co-array question
>
> Hi,
>
> One of our engineers had the following questions about the co-arrays. 
> Can someone from the list answer them?
>
> Does the following program constitute a violation of F’2018 C949 (“The 
> declared type of /source-expr /shall not have a coarray ultimate 
> component.”)?
>
> program main
>
>   type :: type
>
>     integer, allocatable :: coarray[:]
>
>   end type
>
>   type(type), save, target :: object
>
>   class(*), allocatable :: allocatable
>
>   allocate(object%coarray[*]);
>
>   allocate(allocatable, source = object)
>
> end
>
> And is the following in violation of any constraint, or is it now a 
> conforming program?
>
> program main
>
>   type :: type
>
>     integer, allocatable :: coarray[:]
>
>   end type
>
>   type(type), save, target :: object
>
>   class(*), pointer :: pointer
>
>   class(*), allocatable :: allocatable
>
>   allocate(object%coarray[*]);
>
>   pointer => object
>
>   allocate(allocatable, source = pointer)
>
> end
>
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