To: J3                                                     J3/21-112r1
From: T. Clune and M. Haveraaen
Subject: Retract TYPEOF and CLASSOF features
Date: 2021-February-21

#Reference: 21-007

The generics subgroup strongly recommends that the proposed TYPEOF and
CLASSOF features be removed from F202x.  Upon reflection, we have
concluded that these features will become superfluous under the more
powerful generics capabilities planned for F202y and would likely
result in several undesirable consequences.

While we recognize that TYPEOF and CLASSOF could be of some limited
use in implementing certain generics use cases (e.g., containers),
these applications would generally rely heavily on the use of INCLUDE
statements.  This would lead to the situation where:

  - people who pay attention to the Fortran standard will upgrade
    their code to use TYPEOF/CLASSOF/INCLUDE

  - educational materials will be written to explain how to use
    TYPEOF/CLASSOF/INCLUDE to write generic code in Fortran

  - developer tools like IDEs (code aware editors) are currently
    struggling to support INCLUDE, but will have to add extra effort
    to support this form of generics - or give up supporting Fortran

  - people outside of Fortran will become more convinced Fortran is an
    archaic language

Then, when F202y delivers a proper generics mechansism, TYPEOF/CLASSOF
become suprefluous (but not made obsolescent) we envision the
following consequences:

  - code developed with the TYPEOF/CLASSOF/INCLUDE hack will generally
    not be upgraded since the new generic notation will be very
    different from the hack

  - people who search for <<Fortran generics>> will find the old blogs
    with the TYPEOF/CLASSOF/INCLUDE hack and follow this pattern

  - developer tools will need another major upgrade - with IDE
    maintainers wondering if the whimsical behaviour of the Fortran
    committee is worth the investment

  - Fortran becomes a modern language, but will still be perceived as
    an archaic language using INCLUDE for generics