J3/12-121
To: J3
From: Malcolm Cohen
Subject: Interp vector subscript target
Date: 2012 January 30

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NUMBER:
TITLE: Vector subscript target
KEYWORDS: Pointer assignment, Vector subscript
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress

QUESTION:

Consider

  PROGRAM m197006
    REAL,TARGET :: x(100) = [ (i,i=1,100) ]
    REAL,POINTER :: p(:)
    TYPE t
      REAL,POINTER :: q(:)
    END TYPE
    TYPE(t) y
    p => x                     ! (1)
    y = t(x)                   ! (2)
    p => x( [ 1,4,9,25 ] )     ! (3)
    y = t(x( [ 1,4,9,25 ] ))   ! (4)
    PRINT *,y%q
  END PROGRAM

The pointer assignment statement at (1) associates P with X.
The intrinsic assignment statement at (2) includes the effect of
pointer assignment of X to Y%Q, but is not a pointer assignment
statement.

The pointer assignment statement at (3) is not standard-conforming
according to 6.5.3.3.2 paragraph 2:
  "An array section with a vector subscript shall not be
   ... the <data-target> in a pointer assignment statement"

However, the intrinsic assignment statement at (4) is not subject to
this requirement as it is not a pointer assignment statement.

Note that the quoted paragraph is entirely  duplicative, as in:
 - the first bullet item is covered by 12.5.2.4p18,
 - the second bullet item is covered by C724 in 7.2.2.2
   (but C724 does not cover this case either),
 - the third bullet item is covered by C901 in 9.5.1.
Some editorial improvements could be made.

Q1. Was this intended to be allowed?

Q2. If not, was it intended to be prohibited by a constraint like
    C724, or was it intended to be a simple requirement?
    (Editorial note: in any case surely the requirement should appear
    in the pointer assignment subclause.)

ANSWER:

A1. No, this was not intended.  An edit is supplied to correct this.

A2. Constraint C724 was intended to cover this case.  An edit is
    supplied to correct his.

EDIT:

[124:6] 6.5.3.3.2 Vector subscript, paragraph 2, second bullet item,
        Change "the <data-target> in a pointer assignment statement"
        to "the target in pointer assignment (C724)".

[158:19-20] In 7.2.2.2 Syntax of the pointer assignment statement,
            C724, change ""(R737) A <variable>"
            to "A variable that is a pointer target",
            making the whole constraint read:
  "A variable that is a pointer target shall have either the TARGET
   or POINTER attribute, and shall not be an array section with a
   vector subscript."
{Make the constraint apply to all forms of pointer assignment.}

ALTERNATIVE A2:

A2. Constraint C724 was not intended to cover this case, it was
    intended to be a simple requirement.  An edit is supplied to
    clarify this.

ALTERNATIVE EDITS:

[124:6] 6.5.3.3.2 Vector subscript, paragraph 2, second bullet item,
        Change "the <data-target> in a pointer assignment statement"
        to "the target in pointer assignment (7.2.2.3)".

[159:26+] In 7.2.2.3 Data pointer assignment, before paragraph 7
          which begins "If the pointer object has the CONTIGUOUS",
          insert new paragraph
  "The pointer target shall not be an array section with a vector
   subscript."
{Add the prohibition as a simple requirement.}

EDITORIAL (for next revision):

Additional edits are suggested:

[124:4] Change "An" to "Note that an",
        change "shall not be" to "is not permitted to be".
[124:5] After "redefined" insert "(12.5.2.4)".
[124:7] After "file" insert "(C901)".

SUBMITTED BY: Malcolm Cohen

HISTORY: 12-nnn   m197 Submitted

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