[J3] [EXTERNAL] Elemental type-bound functions not useful

[Damian Rouson]

On Mon, Mar 29, 2021 at 6:11 PM Van Snyder via J3 <j3 at mailman.j3-fortran.org>
wrote:

>
> Fortran doesn't yet have "sealed" or "inextensible" types (unless I missed
> something that prevents creating an extension type).
>

One can prevent type extension by declaring a type-bound generic procedure
with the same name as the name of the type as one might do to
effectively write a type-bound, user-defined structure constructor:

type foo
contains
  procedure :: foo_constructor
  generic :: foo => foo_constructor
end type

My thoughts are aligned with those of Tom and Vipul.   Once Fortran
supports generic programming, I suspect it will displace type extension for
most of my purposes. For now, I strive to limit type extension to extending
abstract types. We sometimes have a non-abstract type extending an abstract
type that extends another abstract type, but that's as deep as
our hierarchies go in practice.  We frequently combine type extension with
type-bound operators, but I'm not crazy about the type-guarding that this
approach requires. It feels like the developer is being burdened with
ensuring runtime type safety as a stand-in for compile-time type safety,
which is why I suspect I'll replace type extension with generic
programming.

Damian
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