J3/13-204

To: J3
From: Van Snyder
Subject: Interp concerning mixed-kind character assignment
Date: 2013 December 07

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NUMBER: F08/0087
TITLE: Mixed-kind character assignment
KEYWORDS: Mixed kind, character assignment
DEFECT TYPE: Erratum
STATUS: Under J3 consideration

QUESTION:

Assuming that a Fortran 95 processor supported ISO 10646 kind,
A Fortran 95 program might have included a defined assignment with
arguments of character type, with the first argument of ISO 10646 kind
(if the processor supported it as a nonstandard extension) and the
second argument of default kind, e.g.

module CHAR

  interface ASSIGNMENT ( = )
    module procedure CHAR_ASG
  end interface

  integer, parameter :: ISO_10646 = 42 ! KIND for ISO 10646 character

contains

  subroutine CHAR_ASG ( A, B )
    character(kind=iso_10646,len=*), intent(out) :: A
    character(len=*), intent(in) :: B
    integer :: I
    do i = 1, min(len(a),len(b))
      a(i:i) = achar(iachar(b(i:i)),kind=k)
    end do
    do i = min(len(a),len(b))+1, len(a)
      a(i:i) = achar(iachar(' '), kind=k)
    end do
  end subroutine CHAR_ASG

end module CHAR

In Fortran 2003, intrinsic assignment for character type allows the
<variable> to be of ISO 10646 kind and the <expr> to be of ASCII kind.

The requirements for defined assignment in subclause 12.3.2.1.2 of the
2003 standard, and 12.4.3.4.3 of the 2008 standard, require that the
"arguments shall not conform as specified in Table 7.8."  The example
module therefore does not conform to either the 2003 or 2008 standard.

There is nothing in subclause 1.6 of either the 2003 or 2008 standard to
indicate that the above module would no longer conform.

Was it intended that this module no longer conform?

ANSWER 1

It was intended that this module no longer conform.  Edits to subclause
1.6.3 of the 2008 standard are provided to clarify this.

ANSWER 2

It was intended that this module continue to conform.  Edits to
subclause of 12.4.3.4.3 are provided to allow this module to conform.

EDITS 1

Add a list item within subclause 1.6.3 "Fortran 95 compatibility"
[24:27+]:

o ISO/IEC 1539-1:1997 prohibited mixed-kind intrinsic character
  assignment.  Subclause 7.5.1.6 allowed to define assignment for
  characters with different kind type parameter values.  This standard
  defines intrinsic assignment for characters if <expr> is of ASCII or
  default kind and <variable> is of ISO 10646 kind.  Subclause
  12.4.3.4.3 of this standard prohibits a program to define assignment
  in this case."

EDITS 2

Within subclause 12.4.3.4.3p2 [285:2-3], replace "the declared ...
derived type" with "or the arguments shall neither both be of numeric
type nor both be of logical type.  If the arguments are both of
character type, their kind type parameter values shall differ."

{The second sentence of the replacement is necessary to prevent infinite
recursion.}

SUBMITTED BY: Van Snyder

HISTORY: 13-204    m200  F08/0087 submitted

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