To: J3                                                     11-152
From: Jim Xia
Subject: Interop: Constraints on descriptors and usage
Date: 2011 February 17
References: N1838,11-126, 11-127, 11-128, 11-134,11-143r1,
            11-144r1


DISCUSSION

In view of the changes in paper 11-144r1 as amended, several of the
underlying assumptions in papers on related topics are changed, and
the issues raised there might be automatically resolved.  This paper
summarizes the resulting status of papers 11-126, 11-127, 11-128,
11-134, and 11-143r1.

11-126:
-------

Updating or copying a C descriptor is disallowed by the following
edits in 11-144r1:

"
5.2.7 Use of C descriptors

A C descriptor shall not be initialized, updated or copied other than
by calling the functions specified here. ..."


11-127:
-------

The "redundant restriction" between 5.2.6p2 and 5.2.7p1 is removed by
144r1 (which replaces 5.2.7 from N1838).

Issues raised in 5.2.7 are resolved because 11-144r1 disallows
modification of a C descriptor after its initialization except to use
functions provided in 5.2.6.


11-128:
-------

The proposed edits are included in 11-144r1.


11-134:
-------

The issues raised appear to be covered by 11-144r1.


11-143r1:
---------

a.) assumed-type array issues are resolved

    1.) assumed-shape array is always passed by C descriptor, which
	contains its actual type and elem_len, etc.  So there is no
	issue to index this array in C program.

    2.) explicit-shape array with assumed type is disallowed, and
        further the assumed-size array is required to be of rank 1
        (11-124r3)

    3.) pointer and allocatable are disallowed (11-111r2)

    Summary: For TYPE(*) only assumed-size array (rank 1) can be
    passed using address.  See updated 2.1.

b.) alignment issue in "CASTING" example of A1.3

    option 1: add comment in A1.3 to say "assume the parameter block
           is aligned for casting to integer type."

    option 2: remain silent because the correct alignment is assumed.


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