Re: [RFC, Fortran, (pr66775)] Allocatable function result

[Mikael Morin <mikael dot morin at sfr dot fr>]

Le 10/07/2015 20:57, Steve Kargl a écrit :
> On Fri, Jul 10, 2015 at 06:20:47PM +0200, Mikael Morin wrote:
>>
>> I'm not completely convinced by the standard excerpts that have been
>> quoted about this topic, as they don't have any explicit mention of
>> allocatable variables/expressions.
> 
> I did not quote 12.3.3 about "characteristics of function results",
> which mentions the allocatable attribute.  But, that is not 
> necessarily relevant.  The pieces I quoted explicitly states
> 
>    "On completion of execution of the function, the value returned
>     is that of its function result. ... If the function result is
>     not a pointer, its value shall be defined by the function."
Yeah, well, if the standard committee had allowed unallocated
allocatable results, they would have put it here together with pointer,
I guess.

> 
> The function not only needs to allocate memory, it needs to
> assign it a value.  In the following, if i <= 0, the function
> result is not defined. 
> 
> module foo
>    contains
>    function bar(i)
>       integer, allocatable :: bar
>       integer, intent(in) :: i
>       if (i > 0) bar = i
>    end function bar
> end module foo
> 
> program test
>    use foo
>    integer j
>    j = bar( 3); print *, j
>    j = bar(-3); print *, j
>    end if
> end program test
> 
> Even if Andre developed a patch to allocate memory in
> bar() for the i <= 0 case to prevent the segfault, the
> function must return a value.  What should that value be?
Your example is, of course, 100% invalid; a value is needed to put in j.
But the case is more debatable to me, if j is allocatable.
In that case an unallocated bar() result could just make j unallocated.

Mikael