[J3] Can a procedure pointer have character(*) result type?

Wed Nov 30 23:52:53 UTC 2022

Hi Daniel,

Your assertion that a function pointer is not a function is not supported by any normative text.

Indeed the very definition of “procedure pointer” states that it is a procedure with the POINTER attribute, i.e. all procedure pointers are procedures.

A procedure is either a function (if typed) or a subroutine (which has no type). Thus it follows that a subroutine with the POINTER attribute would be a subroutine pointer, and that a function with the POINTER attribute would be a function pointer.

Note that the constraint has “function name”, thus applies to all named functions. It is not a BNF term limited to some context – it applies to *ALL* functions.

Cheers,

-- 

..............Malcolm Cohen, NAG Oxford/Tokyo.

From: Daniel C Chen <cdchen at ca.ibm.com> 
Sent: Thursday, December 1, 2022 1:24 AM
To: Clune, Thomas L. (GSFC-6101) <thomas.l.clune at nasa.gov>; General J3 interest list <j3 at mailman.j3-fortran.org>; Long, Bill F <william.long at hpe.com>
Cc: Malcolm Cohen <malcolm at nag-j.co.jp>
Subject: RE: [J3] Can a procedure pointer have character(*) result type?

Hi Tom,
I think in R803, the function-name is indeed a function name. However, I don’t think a procedure pointer name is a function name nor it should fall into this rule. I think it should be object-name in this particular BNF. This is also the reason I can’t see C724 applies to procedure pointer. I could be wrong though.
Thanks,
Daniel

From: Clune, Thomas L. (GSFC-6101) <thomas.l.clune at nasa.gov <mailto:thomas.l.clune at nasa.gov> > 
Sent: November 30, 2022 10:35 AM
To: General J3 interest list <j3 at mailman.j3-fortran.org <mailto:j3 at mailman.j3-fortran.org> >; Long, Bill F <william.long at hpe.com <mailto:william.long at hpe.com> >
Cc: Daniel C Chen <cdchen at ca.ibm.com <mailto:cdchen at ca.ibm.com> >; Malcolm Cohen <malcolm at nag-j.co.jp <mailto:malcolm at nag-j.co.jp> >
Subject: Re: [EXTERNAL] Re: [J3] Can a procedure pointer have character(*) result type?

Daniel, I think the constraint does disallow the procedure pointer case. This is a special case of type-declaration-stmt. R801: type-declaration-stmt is declaration-type-spec [ [ , attr-spec ] .. . :: ] entity-decl-list Where R803 entity-decl 

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Daniel,

I think the constraint does disallow the procedure pointer case.     This is a special case of type-declaration-stmt.

R801: type-declaration-stmt is declaration-type-spec [ [ , attr-spec ] ... :: ] entity-decl-list

Where 

R803 entity-decl is object-name [ ( array-spec ) ]

     [ lbracket coarray-spec rbracket ]

    [ * char-length ] [ initialization ]

    or function-name [ * char-length ]

The “or” clause in R803 is the one that applies in C724.   I.e., the POINTER case has a function name that is not necessarily related to that of the target procedure.

Cheers,

*	Tom

From: J3 <j3-bounces at mailman.j3-fortran.org <mailto:j3-bounces at mailman.j3-fortran.org> > on behalf of j3 <j3 at mailman.j3-fortran.org <mailto:j3 at mailman.j3-fortran.org> >
Reply-To: j3 <j3 at mailman.j3-fortran.org <mailto:j3 at mailman.j3-fortran.org> >
Date: Wednesday, November 30, 2022 at 10:11 AM
To: "Long, Bill F" <william.long at hpe.com <mailto:william.long at hpe.com> >, j3 <j3 at mailman.j3-fortran.org <mailto:j3 at mailman.j3-fortran.org> >
Cc: Daniel C Chen <cdchen at ca.ibm.com <mailto:cdchen at ca.ibm.com> >, Malcolm Cohen <malcolm at nag-j.co.jp <mailto:malcolm at nag-j.co.jp> >
Subject: [EXTERNAL] Re: [J3] Can a procedure pointer have character(*) result type?

Hi Bill,
It should be C724 in F2018.
It states:
“C724 A function name declared with an asterisk type-param-value shall not be an array, a pointer, elemental, or pure. A function name declared with an asterisk type-param-value shall not have the RECURSIVE attribute.”

I am not sure how it disallows the procedure pointer case.
Thanks,
Daniel

From: Long, Bill F <william.long at hpe.com <mailto:william.long at hpe.com> > 
Sent: November 30, 2022 9:43 AM
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Cc: Daniel C Chen <cdchen at ca.ibm.com <mailto:cdchen at ca.ibm.com> >; Malcolm Cohen <malcolm at nag-j.co.jp <mailto:malcolm at nag-j.co.jp> >
Subject: [EXTERNAL] Re: [J3] Can a procedure pointer have character(*) result type?

Which version of the standard is this C723 from? Does not look anything like the C723 in either F2018 or N2209. Also, I suspect the omitted .. . text effectively excludes the confusing cases. Cheers, Bill From: J3 <j3-bounces@ mailman. j3-fortran. org> 

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Which version of the standard is this C723 from?   Does not look anything like the C723 in either F2018 or N2209.

Also, I suspect the omitted ... text effectively excludes the confusing cases. 

Cheers,

Bill

  _____  

From: J3 <j3-bounces at mailman.j3-fortran.org <mailto:j3-bounces at mailman.j3-fortran.org> > on behalf of Daniel C Chen via J3 <j3 at mailman.j3-fortran.org <mailto:j3 at mailman.j3-fortran.org> >
Sent: Wednesday, November 30, 2022 3:13 AM
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Cc: Daniel C Chen <cdchen at ca.ibm.com <mailto:cdchen at ca.ibm.com> >; Malcolm Cohen <malcolm at nag-j.co.jp <mailto:malcolm at nag-j.co.jp> >
Subject: Re: [J3] Can a procedure pointer have character(*) result type? 

Hi Malcolm,
C723 states “A function name….shall not be…, a pointer”. Is a procedure pointer name also a function name? It seems unclear to me as its procedure target can also be a subroutine.

Thanks,
Daniel

From: J3 <j3-bounces at mailman.j3-fortran.org <mailto:j3-bounces at mailman.j3-fortran.org> > On Behalf Of Malcolm Cohen via J3
Sent: November 30, 2022 12:21 AM
To: 'General J3 interest list' <j3 at mailman.j3-fortran.org <mailto:j3 at mailman.j3-fortran.org> >
Cc: Malcolm Cohen <malcolm at nag-j.co.jp <mailto:malcolm at nag-j.co.jp> >
Subject: [EXTERNAL] Re: [J3] Can a procedure pointer have character(*) result type?

Daniel writes > The question I have is regarding if a assumed-length dummy procedure pointer is allowed. No, it is not. The constraint > C723 A function name declared with an asterisk type-param-value shall not be an array, a pointer, 

Daniel writes

> The question I have is regarding if a assumed-length dummy procedure pointer is allowed. 

No, it is not.

The constraint

> C723 A function name declared with an asterisk type-param-value shall not be an array, a pointer,

is operational: there is no doubt that a procedure pointer is a pointer, see the definition of pointer:

3.108

pointer

data pointer or procedure pointer

Therefore assumed-length is not permitted.

> From an implementation viewpoint, I don't see a problem with this usage

I do. That comment assumes information that is not necessary to be passed is nonetheless passed. I see no reason to assume all implementations pass unnecessary information unnecessarily. (Individual implementations may have their own reasons for passing extra information.)

> Your example without pointer worked fine with NAG, but I get an internal compiler error (ICE) when you add it back in

There seems to be a missing error test. I will look into it.

***

Finally, I note that assumed-length functions were already obsolescent in Fortran 95. Procedure pointers were only added in Fortran 2003. It is the long-standing policy of the committee that unless there are good reasons to the contrary, obsolescent features will not be enhanced.

So it is not a surprise that we did not add this feature.

Cheers,

-- 

..............Malcolm Cohen, NAG Oxford/Tokyo.

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