To: J3                                                     J3/24-188
From: Malcolm Cohen
Subject: Auto-generic subprograms comment (3) re coarrays
Date: 2024-October-30
References: 24-139r2, 24-168.


1. Introduction

24-139r2 made the simplification of not permitting an auto-generic dummy
argument to be a coarray.

24-168 asks for reconsideration.

This paper is for revisiting the issue.


2. The current syntax (24-139r2)

Syntax part x03 has the following constraint, comment, specification, and
rationale for the decision.

    C8nn A generic dummy argument shall not be a coarray.

    Comment
      Codimension is not mentioned in the requirements, use cases, or
      specifications, but seems like it would add complication. So we
      should prohibit it for now.

    sNN A generic dummy argument cannot be a coarray.

    Reason: This is just a simplification. At a future time we could allow
            this, and we could also allow generic-corank dummy arguments.


3. Proposed in 24-168

24-168 states:

  In N2217, a generic type declaration statement is defined in the form of
  an extension of R801 type-declaration-statement and therefore it allows
  coarrays as generic dummy arguments.

  I cannot imagine any example where coarrays would be a problem. (My only
  concern is regarding the value of MAX_RANK and its derived problems.)

  Logically, a program written with a generic subprogram is equivalent to
  the program written with the corresponding specific subprograms.
  Therefore, I believe that a generic subprogram can allow a coarray as a
  generic dummy argument as long as a non-generic subprogram can allow the
  same coarray as a dummy argument.


4. Subgroup recommendation

Subgroup does not have a strong opinion on the issue.
The current syntax is reasonable, but it is not much of a simplification.


5. The decision

Straw vote:
    (a) disallow coarray dummy arguments auto-generic in rank/type/kind
        (retain the current syntax and constraint, i.e. status quo)
    (b) allow coarray dummy arguments to be auto-generic in rank/type/kind
        (remove the constraint)
    (u) undecided

?

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