I had a funny and somewhat embarrassing experience around the whole issue of structure name spaces.  When types were spreading through C, we had a lot of discussion about whether we should require all programs to call structures with a structure pointer (which would allow a separate name space for structure members of each structure).   We all thought it was a good idea, but the problem was there was a lot of code out there that didn't conform, including a lot of OS code.  As we started to port Unix to the Interdata (a 32-bit machine), the situation became critical.  So I took a deep breath and implemented the following: the compiler would use the old style structure rules until I saw a "new style" structure reference in the code.  At that point I would start to enforce the new rules, which involved translating the symbol table, and starting to complain if the types didn't match.   This was a very ugly hack, and I had inserted many firewalls and assertions to check that the data structures were correct after this translation.

Now, a word about error messages.  The PDP-11 didn't have much memory.  But at the same time it didn't have much of a debugger in those days.  So the main aim was to identify what went wrong in a small number of characters so you could put in print statements and run it again.  This meant that the message produced had to be short but also unique.  I was producing error checks at a great rate in this code and running out of synonyms for "corrupted" in my messages.

I "published" the code, and everything seemed to be working for a couple of days.  Then Ken, who was working on the Interdata file system, tried to compile a structure declaration that contained a sizeof of a structure that was recursively declared inside of the sizeof, and my code gave up the ghost.  Ken came into my office with a strange look on his face and asked "What is a gummy structure?"

----- Original Message -----

From:

"Clem Cole" <clemc@ccc.com>

To:

"Larry McVoy" <lm@mcvoy.com>

Cc:

"TUHS main list" <tuhs@minnie.tuhs.org>, "Noel Chiappa" <jnc@mercury.lcs.mit.edu>

Sent:

Tue, 20 Dec 2016 11:21:41 -0500

Subject:

Re: [TUHS] nm on Third Edition .o files?'

On Tue, Dec 20, 2016 at 11:09 AM, Larry McVoy <lm@mcvoy.com> wrote:

I get that it doesn't scale but man, so nice when reading
code to know that s.st_size is a stat structure.

​Amen!!!​