
GNU Objective C release notes for gcc 2.4
*****************************************

Since gcc 2.3.3 the Objective C as part of gcc has changed a lot.
This document is to explain what has been done, and a little about
how specific features differ from other implementations.  The runtime
has been completely rewritten.  The earlier runtime had several
severe bugs and was rather incomplete.  The compiler has had several
new features added as well.

This is not documentation for Objective C, it is usable to someone
who knows Objective C from somewhere else.


Runtime API functions
=====================

The runtime is moddeled after the NeXT Objective C runtime.  That is,
most functions have semanthics as it is known from the NeXT.  The
names, however, have changed.  All runtime API functions have names
of lowercase letters and and underscores as opposed to the
`traditional' mixed case names.  
	The runtime api functions are not documented as of now.
Someone offered to write it, and did it, but we were not allowed to
use it by his university (Very sad story).  We have started writing
the documentation over again.  This will be announced appropriate
places when it becomes avilable.


Protocols
=========

Protocols are now fully supported. The semanthics is exactly as on the
NeXT.  There is a flag to specify how protocols should be typechecked
when adopted to classes.  The normal typechecker requires that all
methods in a given protocol must be implemented in the class that
adopts it -- it is not enough to inherit them.  The flag
`-Wno-protocol' causes it to allow inherited methods, while
`-Wprotocols' is the default which requires them defined.


+initialize 
===========

This method, if defined, is called before any other instance or class
methods of that particular class.  This method is not inherited, and
is thus not called as initializer for a subclass that doesn't define
it itself.  Thus, each +initialize method is called exactly once (or
never if no methods of that particular class is never called).
Besides this, it is allowed to have several +initialize methods, one
for each category.  The order in which these (multiple methods) are
called is not well defined.  I am not completely certain what the
semathics of this method is for other implementations, but this is
how it works for GNU Objective C.


Passivation/Activation/Typedstreams
===================================

This is supported in the style of NeXT TypedStream's.  Consult the
headerfile Typedstreams.h for api functions.  I (Kresten) have
rewritten it in Objective C, but this implementation is not part of
2.4, it is available from the GNU Objective C prerelease archive. 
   There is one semathic difference worth noting concerning objects
stored with objc_write_object_reference (aka NXWriteObjectReference).
When these are read back in, their object is not guaranteed to be
available until the `-awake' method is called in the object that
requests that object.  To objc_read_object you must pass a pointer to
an id, which is valid after exit from the function calling it (like
e.g. an instance variable).  In general, you should not use objects
read in until the -awake method is called.


argframe manipulation
=====================

performv:: will not work properly on all targets.  A primitive
heuristics is included which tries to determine if and how it should
be done.  You will get a warning when compiling `objc-msg.c' if the
euristics doesn't work.
  Currently there is no notion of the marg_... macros available on the
NeXT.  That is, the arguments to forward:: can only be used to apply
the arguments in the stylle of performv::.  We are working on this.


Acknowledgements
================

The GNU Objective C team: Geoffrey Knauth <gsk@marble.com> (manager),
Tom Wood <wood@next.com> (compiler) and Kresten Krab Thorup
<krab@iesd.auc.dk> (runtime) would like to thank a some people for
participating in the development of the present GNU Objective C.

Paul Burchard <burchard@geom.umn.edu> and Andrew McCallum
<mccallum@cs.rochester.edu> has been very helpful debugging the
runtime.   Eric Herring <herring@iesd.auc.dk> has been very helpful
cleaning up after the documentation-copyright disaster and is now
helping with the new documentation.

Steve Naroff <snaroff@next.com> and Richard Stallman
<rms@gnu.ai.mit.edu> has been very helpful with implementation details
in the compiler.


Prerelease Archive
==================

Intermediate releases, bugfixes and additional other information of
the GNU Objective C will be available from iesd.auc.dk in the
directory /pub/ObjC.


Bug Reports
===========

Please read the section `Submitting Bugreports' of the gcc manual
before you submit any bugs.
