Re: 'withing' problem [code generation]

["David Crocker" <dcrocker@imsltd.com>]

It's not hard to come up with a system that makes the order of C++ include
files unimportant. Our product currently generates C++ (we would like to
generate Ada, which is why I started this thread) so we needed just such a
scheme.

Our solution uses 2 header files for each main file. The phase 1 header file
just contains forward declarations for all the classes declared, then the
phase 2 header file contains the class declarations proper. Each main file
first includes all relevant phase 1 header files (in alphabetical order) and
then all relevant phase 2 header files (also in alphabetical order). The
phase 2 header files include other phase 2 header files only where there is
a strong dependency (i.e. class inheritance). Strong dependencies are not
circular. Of course, we also use the usual header guards to ensure each file
only gets included once.

The nicest solution is the one used by Java (and by our own product) - no
restriction at all on forward referencing classes/types, or on packages
referring to each other (except for absurd cases like 2 classes inheriting
from each other). This is the way all programming languages should go, IMO.
Forward-declarations should be considered obsolete - they only exist to make
life easier for the compiler writer, and compiler technology has come a long
way now.
--
David Crocker, Escher Technologies Ltd. www.eschertech.com


"Mark Johnson" <Mark_H_Johnson@Raytheon.com> wrote in message
news:3BFA6BDC.26E7557E@Raytheon.com...

(snip)

> I thought about this a little last night and you have the circular
dependency problem
> in C if you are not careful. You get an infinite loop in the C
preprocessor if
> doctor.h includes patient.h and vice versa. Almost everybody codes their
header files
> to have some #ifundef that encloses the body of the header file. That way,
each
> header is expanded only once. Even with that, you could have a subtle bug
due to the
> different order of expansion - doctor before patient or patient before
doctor. Icky,
> nasty problems to find and fix..