[J3] Co-array question

[Malcolm Cohen]

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.

 

The pointer can of course be used safely, viz contexts other than as input to SOURCE=.

 

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=.)

 

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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