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author kono
date Fri, 27 Oct 2017 22:46:09 +0900
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1
2 GNU Objective C notes
3 *********************
4
5 This document is to explain what has been done, and a little about how
6 specific features differ from other implementations. The runtime has
7 been completely rewritten in gcc 2.4. The earlier runtime had several
8 severe bugs and was rather incomplete. The compiler has had several
9 new features added as well.
10
11 This is not documentation for Objective C, it is usable to someone
12 who knows Objective C from somewhere else.
13
14
15 Runtime API functions
16 =====================
17
18 The runtime is modeled after the NeXT Objective C runtime. That is,
19 most functions have semantics as it is known from the NeXT. The
20 names, however, have changed. All runtime API functions have names
21 of lowercase letters and underscores as opposed to the
22 `traditional' mixed case names.
23 The runtime api functions are not documented as of now.
24 Someone offered to write it, and did it, but we were not allowed to
25 use it by his university (Very sad story). We have started writing
26 the documentation over again. This will be announced in appropriate
27 places when it becomes available.
28
29
30 Protocols
31 =========
32
33 Protocols are now fully supported. The semantics is exactly as on the
34 NeXT. There is a flag to specify how protocols should be typechecked
35 when adopted to classes. The normal typechecker requires that all
36 methods in a given protocol must be implemented in the class that
37 adopts 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 ===========
44 This method, if defined, is called for each class and category
45 implementation when the class is loaded into the runtime. This method
46 is not inherited, and is thus not called for a subclass that doesn't
47 define it itself. Thus, each +load method is called exactly once by
48 the runtime. The runtime invocation of this method is thread safe.
49
50
51 +initialize
52 ===========
53
54 This method, if defined, is called before any other instance or class
55 methods of that particular class. For the GNU runtime, this method is
56 not inherited, and is thus not called as initializer for a subclass that
57 doesn't define it itself. Thus, each +initialize method is called exactly
58 once by the runtime (or never if no methods of that particular class is
59 never called). It is wise to guard against multiple invocations anyway
60 to remain portable with the NeXT runtime. The runtime invocation of
61 this method is thread safe.
62
63
64 Passivation/Activation/Typedstreams
65 ===================================
66
67 This is supported in the style of NeXT TypedStream's. Consult the
68 headerfile Typedstreams.h for api functions. I (Kresten) have
69 rewritten it in Objective C, but this implementation is not part of
70 2.4, it is available from the GNU Objective C prerelease archive.
71 There is one difference worth noting concerning objects stored with
72 objc_write_object_reference (aka NXWriteObjectReference). When these
73 are read back in, their object is not guaranteed to be available until
74 the `-awake' method is called in the object that requests that object.
75 To objc_read_object you must pass a pointer to an id, which is valid
76 after exit from the function calling it (like e.g. an instance
77 variable). In general, you should not use objects read in until the
78 -awake method is called.
79
80
81 Acknowledgements
82 ================
83
84 The GNU Objective C team: Geoffrey Knauth <gsk@marble.com> (manager),
85 Tom Wood <wood@next.com> (compiler) and Kresten Krab Thorup
86 <krab@iesd.auc.dk> (runtime) would like to thank a some people for
87 participating in the development of the present GNU Objective C.
88
89 Paul Burchard <burchard@geom.umn.edu> and Andrew McCallum
90 <mccallum@cs.rochester.edu> has been very helpful debugging the
91 runtime. Eric Herring <herring@iesd.auc.dk> has been very helpful
92 cleaning up after the documentation-copyright disaster and is now
93 helping with the new documentation.
94
95 Steve Naroff <snaroff@next.com> and Richard Stallman
96 <rms@gnu.ai.mit.edu> has been very helpful with implementation details
97 in the compiler.
98
99
100 Bug Reports
101 ===========
102
103 Please read the section `Submitting Bugreports' of the gcc manual
104 before you submit any bugs.