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+load 43=========== 44This method, if defined, is called for each class and category 45implementation when the class is loaded into the runtime. This method 46is not inherited, and is thus not called for a subclass that doesn't 47define it itself. Thus, each +load method is called exactly once by 48the runtime. The runtime invocation of this method is thread safe. 49 50 51+initialize 52=========== 53 54This method, if defined, is called before any other instance or class 55methods of that particular class. For the GNU runtime, this method is 56not inherited, and is thus not called as initializer for a subclass that 57doesn't define it itself. Thus, each +initialize method is called exactly 58once by the runtime (or never if no methods of that particular class is 59never called). It is wise to guard against multiple invocations anyway 60to remain portable with the NeXT runtime. The runtime invocation of 61this method is thread safe. 62 63 64Passivation/Activation/Typedstreams 65=================================== 66 67This is supported in the style of NeXT TypedStream's. Consult the 68headerfile Typedstreams.h for api functions. I (Kresten) have 69rewritten it in Objective C, but this implementation is not part of 702.4, it is available from the GNU Objective C prerelease archive. 71 There is one difference worth noting concerning objects stored with 72objc_write_object_reference (aka NXWriteObjectReference). When these 73are read back in, their object is not guaranteed to be available until 74the `-awake' method is called in the object that requests that object. 75To objc_read_object you must pass a pointer to an id, which is valid 76after exit from the function calling it (like e.g. an instance 77variable). In general, you should not use objects read in until the 78-awake method is called. 79 80 81Acknowledgements 82================ 83 84The GNU Objective C team: Geoffrey Knauth <gsk@marble.com> (manager), 85Tom Wood <wood@next.com> (compiler) and Kresten Krab Thorup 86<krab@iesd.auc.dk> (runtime) would like to thank a some people for 87participating in the development of the present GNU Objective C. 88 89Paul Burchard <burchard@geom.umn.edu> and Andrew McCallum 90<mccallum@cs.rochester.edu> has been very helpful debugging the 91runtime. Eric Herring <herring@iesd.auc.dk> has been very helpful 92cleaning up after the documentation-copyright disaster and is now 93helping with the new documentation. 94 95Steve Naroff <snaroff@next.com> and Richard Stallman 96<rms@gnu.ai.mit.edu> has been very helpful with implementation details 97in the compiler. 98 99 100Bug Reports 101=========== 102 103Please read the section `Submitting Bugreports' of the gcc manual 104before you submit any bugs. 105