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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
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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
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51+initialize
52===========
53
54This method, if defined, is called before any other instance or class
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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.
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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.