J3/04-310

To: J3
From: Malcolm Cohen
Subject: Interp F90/000140
Date: 5th May 2004

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NUMBER: F90/000140
TITLE: TARGET attribute for a derived-type object with a pointer
       component
KEYWORDS: POINTER attribute, TARGET attribute, structure, structure
          component
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION: Section 6.1.2 (page 63) states:

   "A structure component has the INTENT, TARGET, or PARAMETER
    attribute if the parent object has the attribute."

A constraint following R505 (page 40) states:

   "Constraint: If the POINTER attribute is specified, the TARGET,
    INTENT, EXTERNAL, or INTRINSIC attribute must not be specified."

This would seem to imply that a derived-type object with a pointer
component could not have the TARGET attribute. Though it is
informative, Annex C.4.6 (page 267) contains the following example:

       "TYPE CELL
                INTEGER :: VAL
                TYPE (CELL), POINTER :: NEXT_CELL
        END TYPE CELL
        TYPE (CELL), TARGET :: HEAD
        TYPE (CELL), POINTER :: CURRENT
        ...
        CURRENT => HEAD"

which allows the static head of a linked list or tree.  Does the
structure component HEAD % NEXT_CELL contradict the text cited above
from section 6.1.2 or the cited constraint following R505?

ANSWER: No, the component reference does not contradict either the
constraint or the cited text from 6.1.2.  The cited text from 6.1.2 has been
clarified by F95 interpretation 000100.

Discussion: The constraints that follow a syntax rule, or a set of
syntax rules, are syntactic constraints and apply only to the syntax
rules they immediately follow.  Thus, the constraints that follow
rules R501 through R505 at the beginning of section 5 apply only to
those rules.  This means they apply only to type declaration
statements.  Since a derived type component is part of a derived type
definition (which is not a type declaration statement), the
constraints do not apply to derived type components.  The rule that
prevents an entity from having conflicting attributes when applied by
multiple specification statements is found in 5.2:

  "The combination of attributes that may be specified for a
   particular entity is subject to the same restrictions as for type
   declaration statements regardless of the method of specification."

EDIT: None.

SUBMITTED BY: J. Martin in response to email May 7, 1993 from
              Yukimasa Yoshida

HISTORY: 93-179  m125 canceled, interpretation number then reassigned
         93-181  m125 Response, Withdrawn to remove suggested edit.
         93-223r m126 Response proposed, approved uc
         93-255r1 m127 ballot failed 18-5
         94-339  m131 Revised response proposed, approved 14-2
         95-034r1 m132 X3J3 ballot failed 8-12
         95-033   m132 Revised response, straw vote on intent 5-2-7
         95-092   m132 Revised discussion, approved u.c.
         95-101   m133 X3J3 ballot failed 11-7
         04-310   m168 Revised response.

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