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1
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2 GNU Objective C notes
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3 *********************
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4
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5 This document is to explain what has been done, and a little about how
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6 specific features differ from other implementations. The runtime has
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7 been completely rewritten in gcc 2.4. The earlier runtime had several
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8 severe bugs and was rather incomplete. The compiler has had several
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9 new features added as well.
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10
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11 This is not documentation for Objective C, it is usable to someone
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12 who knows Objective C from somewhere else.
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13
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14
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15 Runtime API functions
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16 =====================
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17
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18 The runtime is modeled after the NeXT Objective C runtime. That is,
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19 most functions have semantics as it is known from the NeXT. The
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20 names, however, have changed. All runtime API functions have names
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21 of lowercase letters and underscores as opposed to the
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22 `traditional' mixed case names.
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23 The runtime api functions are not documented as of now.
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24 Someone offered to write it, and did it, but we were not allowed to
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25 use it by his university (Very sad story). We have started writing
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26 the documentation over again. This will be announced in appropriate
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27 places when it becomes available.
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28
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29
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30 Protocols
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31 =========
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32
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33 Protocols are now fully supported. The semantics is exactly as on the
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34 NeXT. There is a flag to specify how protocols should be typechecked
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35 when adopted to classes. The normal typechecker requires that all
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36 methods in a given protocol must be implemented in the class that
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37 adopts it -- it is not enough to inherit them. The flag
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38 `-Wno-protocol' causes it to allow inherited methods, while
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39 `-Wprotocols' is the default which requires them defined.
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40
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41
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42 +load
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43 ===========
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44 This method, if defined, is called for each class and category
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45 implementation when the class is loaded into the runtime. This method
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46 is not inherited, and is thus not called for a subclass that doesn't
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47 define it itself. Thus, each +load method is called exactly once by
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48 the runtime. The runtime invocation of this method is thread safe.
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49
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50
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51 +initialize
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52 ===========
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53
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54 This method, if defined, is called before any other instance or class
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55 methods of that particular class. For the GNU runtime, this method is
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56 not inherited, and is thus not called as initializer for a subclass that
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57 doesn't define it itself. Thus, each +initialize method is called exactly
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58 once by the runtime (or never if no methods of that particular class is
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59 never called). It is wise to guard against multiple invocations anyway
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60 to remain portable with the NeXT runtime. The runtime invocation of
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61 this method is thread safe.
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62
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63
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64 Passivation/Activation/Typedstreams
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65 ===================================
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66
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67 This is supported in the style of NeXT TypedStream's. Consult the
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68 headerfile Typedstreams.h for api functions. I (Kresten) have
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69 rewritten it in Objective C, but this implementation is not part of
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70 2.4, it is available from the GNU Objective C prerelease archive.
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71 There is one difference worth noting concerning objects stored with
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72 objc_write_object_reference (aka NXWriteObjectReference). When these
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73 are read back in, their object is not guaranteed to be available until
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74 the `-awake' method is called in the object that requests that object.
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75 To objc_read_object you must pass a pointer to an id, which is valid
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76 after exit from the function calling it (like e.g. an instance
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77 variable). In general, you should not use objects read in until the
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78 -awake method is called.
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79
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80
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81 Acknowledgements
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82 ================
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83
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84 The GNU Objective C team: Geoffrey Knauth <gsk@marble.com> (manager),
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85 Tom Wood <wood@next.com> (compiler) and Kresten Krab Thorup
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86 <krab@iesd.auc.dk> (runtime) would like to thank a some people for
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87 participating in the development of the present GNU Objective C.
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88
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89 Paul Burchard <burchard@geom.umn.edu> and Andrew McCallum
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90 <mccallum@cs.rochester.edu> has been very helpful debugging the
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91 runtime. Eric Herring <herring@iesd.auc.dk> has been very helpful
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92 cleaning up after the documentation-copyright disaster and is now
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93 helping with the new documentation.
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94
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95 Steve Naroff <snaroff@next.com> and Richard Stallman
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96 <rms@gnu.ai.mit.edu> has been very helpful with implementation details
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97 in the compiler.
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98
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99
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100 Bug Reports
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101 ===========
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102
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103 Please read the section `Submitting Bugreports' of the gcc manual
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104 before you submit any bugs.
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