11-163
To: J3
From: Nick Maclaren
Subject: Interop TR: the version member
Date: 2011 June 07
Reference: N1854


There is a lack of clarity about when the version member is set, and
this is particularly serious to do with CFI_section and CFI_select_part,
which can be used on either new or existing descriptors but which have
no way of telling which they have!  The problem affects ONLY pointers,
and is with code like:

    SUBROUTINE Fred (arg) BIND(C)
        INTEGER, POINTER, DIMENSION(:,:,:), INTENT(OUT) :: arg
    END SUBROUTINE Fred
    INTEGER, POINTER, DIMENSION(:,:,:) :: ptr
    CALL Fred(arg)

The Fortran code may well get back a descriptor that has a newer version
than it created the pointer with.  In itself, that does not matter, but
it handicap when using the version for extensions.  There are a couple
of reasonable options.

Option 1:

We specify that the version member is set on establishment (i.e. always
by CFI_establish, CFI_section and CFI_select_part, and never by other
calls).  That is clear and simple.

Option 2:

We require that CFI_establish is called before CFI_section and
CFI_select_part, and simplify those by removing the arguments that
will then not be needed.

On the grounds of minimal change, I propose the first.


Edits to N1854:

[10:7] Append "when the descriptor is established and otherwise not
changed."