J3/15-127
To:        J3
From:      Van Snyder
Subject:   Interpretation concerning CLASS and prior type definition
Date: 2015 February 09

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NUMBER: TBD
TITLE: Is CLASS(type) required to refer to a prior type definition?
KEYWORDS: CLASS, type definition
DEFECT TYPE: Interpretation
STATUS: J3 consideration in progress

QUESTION:

Does the CLASS(T) declaration of X in the following conform?

recursive subroutine S ( N, X )
  integer :: N
  class(t), optional :: X
  type :: T
    integer :: Q
  end type T
...

ANSWER (1):

Subclause 4.3.1.3 does not require the <derived-type-spec> in a CLASS
specifier to refer to a previously-defined type.  Therefore the
declaration conforms.

It was intended that CLASS declarations with <derived-type-spec> be
parallel to TYPE declarations.  In a TYPE declaration (4.3.1.2), the
specified derived type is required to be previously defined, or
accessed by use or host association.  Therefore the example ought not
to conform.  Edits are provided to correct this oversight.

ANSWER (2):

Subclause 4.3.1.3 does not require the <derived-type-spec> in a CLASS
specifier to refer to a previously-defined type.  Therefore the
declaration conforms.

Since an object declared with a CLASS specifier must be a pointer,
allocatable, or dummy argument, the same sort of circular dependence,
involving components, against which it is necessary to protect by
requiring prior definition of a type referenced in a TYPE specifier
(other than for pointer or allocatable components) is not possible.
Therefore, prior definition of the type is not necessary, and the
example was intended to conform.

EDITS (1):

[12-007:6+ 4.3.1.3p1+] Insert a paragraph:

"Where a data entity other than a component is declared explicitly using
the CLASS specifier to be of derived type, the specified derived type
shall have been defined previously.  If the data entity is a function
result, the derived type may be specified in the FUNCTION statement
provided the derived type is defined within the body of the function or
is accessible there by use or host association.  If the derived type is
specified in the FUNCTION statement and is defined within the body of
the function, it is as if the function result variable were declared
with that derived type immediately following the <derived-type-def> of
the specified derived type."

{This is essentially identical to 4.3.1.2p1, except for the replacement
of "TYPE" with "CLASS" and the addition of "other than a component"
(4.3.1.2p1 does not mention components, but it ought to because
otherwise it would contradict C440).}

EDITS (2):

None.

SUBMITTED BY: Van Snyder

HISTORY: 15-xxx    m206  F08/nnnn submitted

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