To: J3                                                     J3/23-236r1
From: Tom Clune
Subject: Templates in CONTAINS section
Date: 2023-October-18

Reference: 23-155r2

1. Introduction
===============

One awkwardness of the proposed syntax for templates is that template
procedures appear before the CONTAINS section within a host module.
The awkwardness is compounded in the case of nested templates which
then have the procedures of inner templates appear before the CONTAINS
section of the outer template.

Recently generics subgroup considered the possibility of altering the
proposed syntax to have template definitions appear in the CONTAINS
section of their hosting scope rather than in the specification
section as is the case now.

MODULE  A

   INSTANTIATE T(REAL)

CONTAINS

   TEMPLATE OUTER(T)
       TYPE, DEFERRED :: T
       INSTANTIATE INNER(N=1)
   CONTAINS
      TEMPLATE INNER(N)
         INTEGER, CONSTANT :: N
      CONTAINS
         SUBROUTINE S(x)
	     TYPE(T), RANK(N), INTENT(INOUT) ::  x
	     ...
	 END SUBROUTINE S
      END TEMPLATE INNER

      SUBROUTINE G(x)
         TYPE(T), INTENT(INOUT) :: x

         TYPE(T) :: y(1)

         y = SPREAD(x, 1)
	 CALL S(y)
	 ...
      END SUBROUTINE G
   END TEMPLATE OUTER
END MODULE A


Subgroup was weakly in favor of this change, but would prefer to
solicit the opinion of others before introducing such a change.



2. Straw vote
=============

Should template syntax be modified to place template definitions in
the CONTAINS section rather than the specification of the hosting scope?

  Yes: TEMPLATES should be defined in the CONTAINS section of the
       encompassing scope. Appropriate changes will be made to
       generics syntax.

  No:  TEMPLATES should be defined in the specification section of the
       encompassing scope.  No change to generics syntax.

  Abstain:


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