08-235r2
To: J3
From: Michael Ingrassia
Subject: Public Comment J32021
Date: 2008 August 14

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Commenter: Robert Corbett
Subject: "Allow compatible specific interfaces"

Constraint C1201 in Section 12.4.3.2 of the Fortran 2008
draft is detested by many users.  That constraint should
be eliminated.  The standard already requires that the
characteristics specified by the interface body must
match those of the subprogram definition (see paragraph 7
of Section 12.4.3.2).  That requirement should be
elevated to a constraint for this specific case.
Constraint C1201 might be replaced with

       c1201 (R1201)  If an interface block contains an
             interface-body for a procedure defined by
             that subprogram, the characteristics of the
             specific interface defined by the
             interface-body shall be consistent with
             those specified in the procedure definition
             except that the interface may specify a
             procedure that is not pure if the
             procedure is defined to be pure.

Some users write modules containing interface blocks
describing the external procedure used in their program.
They then use that module in all the external subroutines
and functions in their program.  Most of them have by
now learned to use renaming to avoid problems with
constraint C1201, but they don't like it.  They would
like the information from the interface block created
for a procedure to be visible and used for checking in
the subprogram that defines that procedure.

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J3 response:

J3 agrees this would be a useful feature.  The proposed constraint is not, on
its own, adequate.  J3 has identified some editorial changes that would
be necessary to implement this feature (see 08-235r1), but J3 is not
confident that all necessary changes have been identified at this time.

Since SUBROUTINE and FUNCTION are optional on END statements for module
procedures in the current draft, a better solution for the illustrative
problem the commenter presented is to create module procedures from
external procedures by using INCLUDE lines.