Meissner examples - the last one to fall

[Richard E Maine]

On Oct 4, 2005, at 6:49 AM, Paul THOMAS wrote:

>> Error: 'rect_inductor' is a PRIVATE type and cannot be a dummy 
>> argument of 'mutual_ind_quad_cir_coil', which is PUBLIC at (1)
>> In file induct.f90:1824
>
> Yes, I seem not to have understood what comprises a PRIVATE type in 
> this context, or I have screwed up the implementation.

I didn't go look at induct.f90 to check the context, but the definition 
of a PRIVATE type in that context is *very* subtle. I recall the 
longish J3 discussions about the related interps. The short version 
(omitting all the supporting rationale, which goes on for a bit) is 
that a type is only private if it has the private attribute in the 
module where it is originally defined. If you import (va USE) a type 
into some other module and declare it private there, that doesn't 
actually make the type private - that just means that the second module 
doesn't "export" it. The language keyword PRIVATE is unfortunately 
misleading in that it doesn't mean private. In the words of the 
standard (or close to them - I didn't go find and copy the exact ones, 
but I recall them pretty well from the long debate), the private 
attribute means that the entity "is not a public entity of this 
module". Note the peculiar negative form. Why does it talk about not 
being public instead of about being private? That's because it might 
still be public from some other module. Indeed, it must have been if 
you managed to get it via USE in the first place. Only if it is 
declared private in the original module is it really private.

P.S. Most of this nitpicking is made irrelevant in f2003. In fact, I 
had to go check to make sure it was f2003 instead of f95. Alas, it 
isn't until f2003, so one still has to deal with it in f95. The whole 
constraint in question is "silly". It achieves nothing useful, 
invalidates perfectly sensible code (even after you interpret it 
correctly), and is based on a fundamental misconception of what 
accessibility is about. F2003 removes the silly restriction (and a few 
related ones).

-- 
Richard Maine                |  Good judgment comes from experience;
Richard.Maine@nasa.gov       |  experience comes from bad judgment.
                             |        -- Mark Twain