libobjc/README - gcc.git - Git at Google



            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.


            +load

            
            ===========

            
            This method, if defined, is called for each class and category

            
            implementation when the class is loaded into the runtime.  This method

            
            is not inherited, and is thus not called for a subclass that doesn't

            
            define it itself.  Thus, each +load method is called exactly once by

            
            the runtime.  The runtime invocation of this method is thread safe.


            +initialize

            
            ===========


            This method, if defined, is called before any other instance or class

            
            methods of that particular class.  For the GNU runtime, 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 by the runtime (or never if no methods of that particular class is

            
            never called).  It is wise to guard against multiple invocations anyway

            
            to remain portable with the NeXT runtime.  The runtime invocation of

            
            this method is thread safe.


            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 <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.


            Bug Reports

            
            ===========


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

            
            before you submit any bugs.

	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.


	+load
	===========
	This method, if defined, is called for each class and category
	implementation when the class is loaded into the runtime. This method
	is not inherited, and is thus not called for a subclass that doesn't
	define it itself. Thus, each +load method is called exactly once by
	the runtime. The runtime invocation of this method is thread safe.


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

	This method, if defined, is called before any other instance or class
	methods of that particular class. For the GNU runtime, 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 by the runtime (or never if no methods of that particular class is
	never called). It is wise to guard against multiple invocations anyway
	to remain portable with the NeXT runtime. The runtime invocation of
	this method is thread safe.


	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 <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.


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

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