To: J3                                                     J3/24-169
From: Malcolm Cohen
Subject: US-23/DIN-4: Generic processing of assumed-rank objects, overview
Date: 2024-October-21
Reference: 24-136r1


1. Introduction

This paper reviews the current state of the US-23/DIN-4 proposals, and
suggests splitting them into three separate proposals which are independent
of each other.

This is not to make new WG5 proposals, merely to improve the organisation
of this one.

It should also be noted that there is some potential interaction between
these features and US-07 "Improve rank-independent functionality", and also
US-24 "Rank-independent looping".


2. The proposals

(1) DIN-4I: intrinsics.

    All of the proposals here are problematic when an assumed-rank array is
    associated with an assumed-size array. Thus, they are subject to
    agreement being reached on what to do in that case.

    (a) Permit whole array reduction intrinsics of an assumed-rank array;
        that is, an array reduction with no DIM argument.
        These are ALL, ANY, IALL, IANY, IPARITY, MAXVAL, MINVAL, PRODUCT,
        PARITY, REDUCE, SUM.
        Some of these have an optional MASK argument, which might also be
        problematic.

    (b) Permit the whole array location intrinsics (these work in a very
        similar way to the reductions), again, no DIM argument.
        These are MAXLOC, MINLOC, and FINDLOC.
        Similarly, the optional MASK argument might be problematic.

    (c) Permit the LOGICAL->INTEGER reduction intrinsic COUNT, when there
        is no DIM argument.

    (d) Permit the array transformation intrinsic RESHAPE, when there is no
        PAD argument. Consistency might imply that we should allow RESHAPE
        of an assumed-size array in the same situation.

    (e) Permit the C_LOC function from the intrinsic module ISO_C_BINDING
        to be used with an assumed-rank target.

(2) Proposal DIN-4M: Miscellaneous

    These are, of course, all subject to no technical problem being found.
    And also whether they are agreed to be actually useful.

    (a) As the target in a rank-remapping pointer assignment.

    (b) As the selector in a SELECT TYPE construct.
        This would necessarily expand the concept of assumed-rank to
        include an associate-name that is associated with assumed-rank.

    (c) If contiguous, as the actual argument for sequence association.

(3) Proposal DIN-4X: Axxessing and traversing.

    (a) Syntax for traversing an assumed-rank array, presumably the same
        syntax could be used for rank-independent looping, and so this one
        needs to be developed in conjunction with US-07 and US-24.

    (b) Syntax for accessing an element of an assumed-rank array, possibly
        the same syntax we already use for rank-independent accesses.


3. Formal requirements

For each of the three proposals, a separate paper will be submitted for the
formal requirements.

===END===