Re: [ferret_users] MULTI-FILE NETCDF DATA SET

[Ryo Furue <furue@xxxxxxxxxx>]

Martin,

| The $-form is an old f77 form - as far as I know. It is still
| supported but not required by some compilers, for example xlf.

Yes, you can say that it's an old F77 form, but more precisely,
it was a form that was sometimes used by SOME F77 implementations
AS AN EXTENSION.  That is, it was NOT part of the Fortran 77
standard.

This isn't a nitpicking; it's an important distinction.
If a feature was in the Fortran 77 standard, ALL compilers
that called themselves "Fortran 77" were obliged to implement
it.  The feature in question, namely namelist, was not
part of the F77 standard.  Therefore, some F77 compilers
supported it but others didn't.

There are some implications of this fact.

1) There is no guarantee that the implementations
   that currently support the $-form will continue
   to do so.  Since it was not and is not in the Standard,
   implementations are free to drop it.

2) It is highly unlikely that implementations which
   currently don't support it will do so in the future,
   because there's already a standard-conforming alternative
   (the &-form).

The same applies to any non-standard features. 

Regards,
Ryo