libobjc/README - gcc - 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.