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GNU Objective C notes

*********************

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 in gcc 2.4.  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 modeled after the NeXT Objective C runtime.  That is,

most functions have semantics as it is known from the NeXT.  The

names, however, have changed.  All runtime API functions have names

of lowercase letters 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 in appropriate

places when it becomes available.

Protocols

=========

Protocols are now fully supported.  The semantics 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

semantics 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 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.

Acknowledgements

================

The GNU Objective C team: Geoffrey Knauth  (manager),

Tom Wood  (compiler) and Kresten Krab Thorup

 (runtime) would like to thank a some people for

participating in the development of the present GNU Objective C.

Paul Burchard  and Andrew McCallum

 has been very helpful debugging the

runtime.   Eric Herring  has been very helpful

cleaning up after the documentation-copyright disaster and is now

helping with the new documentation.

Steve Naroff  and Richard Stallman

 has been very helpful with implementation details

in the compiler.

Bug Reports

===========

Please read the section `Submitting Bugreports' of the gcc manual

before you submit any bugs.