1 2GNU Objective C notes 3********************* 4 5This document is to explain what has been done, and a little about how 6specific features differ from other implementations. The runtime has 7been completely rewritten in gcc 2.4. The earlier runtime had several 8severe bugs and was rather incomplete. The compiler has had several 9new features added as well. 10 11This is not documentation for Objective C, it is usable to someone 12who knows Objective C from somewhere else. 13 14 15Runtime API functions 16===================== 17 18The runtime is modeled after the NeXT Objective C runtime. That is, 19most functions have semantics as it is known from the NeXT. The 20names, however, have changed. All runtime API functions have names 21of lowercase letters and underscores as opposed to the 22`traditional' mixed case names. 23 The runtime api functions are not documented as of now. 24Someone offered to write it, and did it, but we were not allowed to 25use it by his university (Very sad story). We have started writing 26the documentation over again. This will be announced in appropriate 27places when it becomes available. 28 29 30Protocols 31========= 32 33Protocols are now fully supported. The semantics is exactly as on the 34NeXT. There is a flag to specify how protocols should be typechecked 35when adopted to classes. The normal typechecker requires that all 36methods in a given protocol must be implemented in the class that 37adopts it -- it is not enough to inherit them. The flag 38`-Wno-protocol' causes it to allow inherited methods, while 39`-Wprotocols' is the default which requires them defined. 40 41 42+initialize 43=========== 44 45This method, if defined, is called before any other instance or class 46methods of that particular class. This method is not inherited, and 47is thus not called as initializer for a subclass that doesn't define 48it itself. Thus, each +initialize method is called exactly once (or 49never if no methods of that particular class is never called). 50Besides this, it is allowed to have several +initialize methods, one 51for each category. The order in which these (multiple methods) are 52called is not well defined. I am not completely certain what the 53semantics of this method is for other implementations, but this is 54how it works for GNU Objective C. 55 56 57Passivation/Activation/Typedstreams 58=================================== 59 60This is supported in the style of NeXT TypedStream's. Consult the 61headerfile Typedstreams.h for api functions. I (Kresten) have 62rewritten it in Objective C, but this implementation is not part of 632.4, it is available from the GNU Objective C prerelease archive. 64 There is one difference worth noting concerning objects stored with 65objc_write_object_reference (aka NXWriteObjectReference). When these 66are read back in, their object is not guaranteed to be available until 67the `-awake' method is called in the object that requests that object. 68To objc_read_object you must pass a pointer to an id, which is valid 69after exit from the function calling it (like e.g. an instance 70variable). In general, you should not use objects read in until the 71-awake method is called. 72 73 74Acknowledgements 75================ 76 77The GNU Objective C team: Geoffrey Knauth <gsk@marble.com> (manager), 78Tom Wood <wood@next.com> (compiler) and Kresten Krab Thorup 79<krab@iesd.auc.dk> (runtime) would like to thank a some people for 80participating in the development of the present GNU Objective C. 81 82Paul Burchard <burchard@geom.umn.edu> and Andrew McCallum 83<mccallum@cs.rochester.edu> has been very helpful debugging the 84runtime. Eric Herring <herring@iesd.auc.dk> has been very helpful 85cleaning up after the documentation-copyright disaster and is now 86helping with the new documentation. 87 88Steve Naroff <snaroff@next.com> and Richard Stallman 89<rms@gnu.ai.mit.edu> has been very helpful with implementation details 90in the compiler. 91 92 93Bug Reports 94=========== 95 96Please read the section `Submitting Bugreports' of the gcc manual 97before you submit any bugs. 98