[J3] [EXTERNAL] Re: Clarification on F18/017

[Carlson, Neil]

Thomas wrote:
> What is really needed to further the argument is a concrete example in which the undesired order will lead to a surprising (or incorrect) result _beyond_ merely the order being surprising.    E.g., some handle to a non Fortran resource is obliterated before the resource is properly released.

Yes, that is exactly the case described at this link already mentioned several times in this thread: https://github.com/j3-fortran/fortran_proposals/issues/146#issuecomment-589857885

But for clarity here is a code skeleton for the described case.  Here amrex is a third party library written in C++ that provides a Fortran interface.  It is a framework that must be started and stopped and its objects depend on that framework. The amrex-provided class amrex_obj is finalizable.  Stopping the framework obliterates resources that its finalizer needs, and so it must be finalized before the framework is stopped.

module m

  use amrex_module

  type :: amrex_env
  contains
    final :: finalize_amrex_env
  end type

  type, extends(amrex_env) :: solver
    class(amrex_obj), allocatable :: obj
  contains
    procedure :: init
  end type

contains

  subroutine finalize_amrex_env(this)
    type(amrex_env), intent(inout) :: this
    call amrex_finalize()
  end subroutine

  subroutine solver_init(this)
    class(solver), intent(out) :: this
    call amrex_init()
    call amrex_alloc_obj(this%obj)
  end subroutine

end module

program main
  use m
  call run
contains
  subroutine run
    type(solver) :: s
    call s%init
  end subroutine
end program

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