[J3] Instead of += etc

[Clive Page]

On 01/11/2018 20:56, Bill Long via J3 wrote:
> 
>> On Nov 1, 2018, at 4:38 AM, Anton Shterenlikht via J3 <j3 at mailman.j3-fortran.org> wrote:
>> On the other hand, at the same meeting
>> there was some angry reaction
>> from the users on the J3 decision
>> to reject auto (re)allocation on READ,
>> despite it scoring high in N2147.
>> The justification given in
>> https://j3-fortran.org/doc/year/18/minutes215.txt
>> was seen too harsh and dismissive by some:
>>
>>        18-135  "Use cases for unallocated list item in READ statement"
>>                 This was broken out from allocatables in ERRMSG, IOMSG.
>>                 Discussion items:  Definite performance issue, as it
>>                 would require double-reading.   Appreciate the goal, but
>>                 seems unrealistic.  List directed could be a problem.
>>                 Format reversion would be a problem. Simple would be
>>                 valuable, but complicated could be very complicated
>>                    SV:  0 - 8 - 4
>>
>> They wonder why a limited "simple” facility
> 
> It is not clear what is meant by “simple” here.

Well maybe I can try to answer this, as I was one of those supporting the feature and indeed, if I remember correctly, it was my question that started the discussion of the issue at the recent BCS Fortran meeting.

I think what "simple" means is whatever it is that compiler-writers determine can be done without excessive effort.  I can see that supporting format reversion and list-directed reads might add considerable complication, but not being a compiler-writer I have no idea really what's easy and what is hard.   But I note that some existing I/O features have been introduced initially in a restricted form, which is better than nothing, and then the restrictions removed in a later standard.  A trivial example: read with SIZE was originally only allowed if the read statement also contained ADVANCE="NO", but it has now been possible to remove that restriction.  I'd have thought that if a read could be used with a scalar character variable of allocatable length in a formatted and not list-directed read without format reversion, and have its size set automatically, just as if that variable had been set in a scalar character assignment statement, that would still be seen as a useful facility.

Regards

-- 
Clive Page