Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!yale!cs.yale.edu!jellinghaus-robert
From: jellinghaus-robert@CS.Yale.EDU (Rob Jellinghaus)
Newsgroups: comp.lang.eiffel
Subject: How to use @ with attribute?
Message-ID: <18296@cs.yale.edu>
Date: 8 Mar 90 09:05:13 GMT
Sender: news@cs.yale.edu
Reply-To: jellinghaus-robert@CS.Yale.EDU (Rob Jellinghaus)
Organization: Yale University Computer Science Dept, New Haven CT  06520-2158
Lines: 50

A short while ago, I attempted to post an article in which I decried Eiffel's
lack of a class which would allow me to store and retrieve objects from 
memory, rather than to/from a file.  I am attempting to integrate Eiffel with
a networking utility, and I want to be able to store arbitrary Eiffel objects
in a structure which can be passed between machines.  The STORABLE class does
what I want to do, but it can only read or write to disk, not to a buffer in
memory.  So rather than wait for ISE to add a store_to_memory function to the
STORABLE class, I am implementing my own, by hacking the code in the _store.c
and _retrieve.c files in /usr/licensed/Eiffel/files.  And it's going well,
except for this latest problem:

I want to pass the address of a particular (integer) field of an object to
a C routine I've written.  The class looks something like this:

class STORED_OBJECT
	...
feature
	hash_value: INTEGER;
	hash is
		external
			hash_object(current_obj: ANY, hash_val: ANY)
				language "C"
		do
			hash_object(Current, @hash)
		end
end -- stored_object

The idea is that I want my hash_object function to be able to reference
the hash field of my Current object.  But when I try to compile this code,
it gives me:

Pass 1 on class stored_object
...
C-compiling stored_object
"stored_object.c": line 125: unacceptable operand of &
es: C-compilation canceled

Why is this?  Changing the declaration of hash_val from ANY to INTEGER doesn't
help.  Removing the @ sign in the call to hash_object removes the error, so
I _know_ there's something wrong with the compiler or with my understanding
of the @ operator.

Can someone at ISE or elsewhere please help me out?  I will have to hack
around this in an ugly way if I don't get an answer.  Thanks for any advice.


Rob Jellinghaus                | "Next time you see a lie being spread or a
jellinghaus-robert@CS.Yale.EDU |  bad decision being made out of sheer ignor-
ROBERTJ@{yalecs,yalevm}.BITNET |  ance, pause, and think of hypertext."
{everyone}!decvax!yale!robertj |     -- K. Eric Drexler, _Engines of Creation_