To: J3                                                     J3/21-146
From: Jon Steidel
Subject: Request for interpretation: Specification inquiry
Date: 2021-June-11

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NUMBER: F18/028
TITLE: Specification inquiry
DEFECT TYPE: Erratum
STATUS: J3 submitted meeting 224
QUESTION:

Consider the following program:
      implicit type (t) (a-z)
      integer,parameter :: n = storage_size(x)
      type t
        character(len=n) :: s
      end type t
      print *, n
      end

Two compilers tested issue a compile time error message while a third
compiler compiled the program and printed "0" when executed.

Is the use of storage_size(x) a valid specification expression
in this program?

DISCUSSION:

In the above program, x is implicitly typed to be type(t). It is used
in a specification expression requiring knowledge of type(t), prior to
the specification of type(t). There is no text in the standard to
prohibit this usage.

The rules for specification expressions require the type, type
parameters, array bounds, and cobounds of a variable to be known
via prior specification, or use or host association when the variable
is used in a specification expression. If an element of an array whose
value is used in a specification expression, the array must be fully
specified in prior declarations.

The intent is that specification expressions which are constant ex-
pressions can be evaluated when seen.

ANSWER:

No, the program is not conforming. The use of an implicitly typed var-
iable of derived type in a specification inquiry prior to the spec-
ification of the derived type was overlooked.  An edit is provided
to correct this oversight.

EDIT to 18-007r1:

[158:4] 10.1.11 Specification expression p6
  Insert at the end of the paragraph:
  "If a variable in a specification expression is typed by the implicit
   typing rules and has a type that is a derived type, that type shall
   be previously defined."

SUBMITTED BY: Jon Steidel

HISTORY: 21-nnn   m224  Submitted

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