NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/lang/fortran/4702

Text File | 1992-12-14 | 2.2 KB | 54 lines

Newsgroups: comp.lang.fortran
Path: sparky!uunet!zaphod.mps.ohio-state.edu!malgudi.oar.net!caen!hellgate.utah.edu!lanl!cochiti.lanl.gov!jlg
From: [e-mail] (J. Giles)
Subject: Re: function name as an argument
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Los Alamos National Laboratory
References: <[e-mail]> <[e-mail]> <[e-mail]>
Date: Mon, 14 Dec 1992 21:53:49 GMT
Lines: 42

In article <[e-mail]>, [e-mail] (J. Giles) writes:
|> [...]
|> Once again: there is no need to rely on dynamic memory to provide
|> the above functionality.  However, it appears that there *is* a
|> constraint in the Fortran 77 standard which prohibits it.  I don't
|> know why and neither does our representative to the committee.

Finally, someone who thinks rather than just reacting has sent me
the answer to this.  The example under discussion in this thread
did *not* require any dynamic memory allocation (or even stack).
However, an similar example would:

      subroutine asub(func, var)
      character*(*) func, var
      ...
      var = other_fcn(func(1), func(2))
      ...
      end

Any example in which the passed-in function would be called more than
once in a single statement would require that more than one chunk of
intermediate space be reserved.  This is apparently the reason for the
constraint in the standard.  No thanks to those whose responses just
echoed the party line with no thought or explanation given.  Thanks
for the correct answer are due to Peter Montgomery of Oregon State.

Of course, a weaker constraint that allowed functions with passed-in
lengths to be used, but only if they were limited to one call per
statement, would also be possible.  It's not clear this was ever
even considered (such a subtle constraint would probably be confusing
anyway).

The Fortran 90 standard allows automatic and dynamic allocation and
should have no problem eliminating the constraint altogether.  And,
indeed, I cannot find any mention of such a constraint in the Fortran 90
document.

Thanks once again to Peter Montgomery for setting me straight on this
issue.

--
J. Giles