|
1 " |
|
2 COPYRIGHT (c) 1988-92 by Claus Gittinger |
|
3 All Rights Reserved |
|
4 |
|
5 This software is furnished under a license and may be used |
|
6 only in accordance with the terms of that license and with the |
|
7 inclusion of the above copyright notice. This software may not |
|
8 be provided or otherwise made available to, or used by, any |
|
9 other person. No title to or ownership of the software is |
|
10 hereby transferred. |
|
11 " |
|
12 |
|
13 Object subclass:#UndefinedObject |
|
14 instanceVariableNames:'' |
|
15 classVariableNames:'' |
|
16 poolDictionaries:'' |
|
17 category:'Kernel-Objects' |
|
18 ! |
|
19 |
|
20 UndefinedObject comment:' |
|
21 |
|
22 COPYRIGHT (c) 1988-92 by Claus Gittinger |
|
23 All Rights Reserved |
|
24 |
|
25 there is only one instance of this class: nil |
|
26 |
|
27 %W% %E% |
|
28 '! |
|
29 |
|
30 !UndefinedObject class methodsFor:'instance creation'! |
|
31 |
|
32 basicNew |
|
33 "catch new - there MUST be only one nil in the system" |
|
34 |
|
35 ^ nil |
|
36 ! |
|
37 |
|
38 basicNew:size |
|
39 "catch new - there MUST be only one nil in the system" |
|
40 |
|
41 ^ nil |
|
42 ! ! |
|
43 |
|
44 !UndefinedObject methodsFor:'error catching'! |
|
45 |
|
46 basicAt:index |
|
47 "catch array access - its illegal |
|
48 defined here since basicAt: in Object ommits the nil-check" |
|
49 |
|
50 ^ self notIndexed |
|
51 ! |
|
52 |
|
53 at:index |
|
54 "catch array access - its illegal |
|
55 defined here since at: in Object ommits the nil-check" |
|
56 |
|
57 ^ self notIndexed |
|
58 ! |
|
59 |
|
60 basicAt:index put:anObject |
|
61 "catch array access - its illegal |
|
62 defined here since basicAt:put: in Object ommits the nil-check" |
|
63 |
|
64 ^ self notIndexed |
|
65 ! |
|
66 |
|
67 at:index put:anObject |
|
68 "catch array access - its illegal |
|
69 defined here since at:put: in Object ommits the nil-check" |
|
70 |
|
71 ^ self notIndexed |
|
72 ! ! |
|
73 |
|
74 !UndefinedObject methodsFor:'testing'! |
|
75 |
|
76 isNil |
|
77 "return true if I am nil - since I am, return true" |
|
78 |
|
79 ^ true |
|
80 ! |
|
81 |
|
82 notNil |
|
83 "return true if I am not nil - since I am nil, return false" |
|
84 |
|
85 ^ false |
|
86 ! |
|
87 |
|
88 size |
|
89 "return the number of indexed instvars |
|
90 defined here since size in Object ommits the nil-check" |
|
91 |
|
92 ^ 0 |
|
93 ! |
|
94 |
|
95 basicSize |
|
96 "return the number of indexed instvars |
|
97 defined here since size in Object ommits the nil-check" |
|
98 |
|
99 ^ 0 |
|
100 ! |
|
101 |
|
102 hash |
|
103 "return an integer useful as a hash key" |
|
104 |
|
105 ^ 0 |
|
106 ! |
|
107 |
|
108 identityHash |
|
109 "return an integer useful as a hash key" |
|
110 |
|
111 ^ 0 |
|
112 ! ! |
|
113 |
|
114 !UndefinedObject methodsFor:'copying'! |
|
115 |
|
116 shallowCopy |
|
117 "return a shallow copy of myself |
|
118 - since there is only one nil in the system return self" |
|
119 |
|
120 ^ self |
|
121 ! |
|
122 |
|
123 deepCopy |
|
124 "return a deep copy of myself |
|
125 - since there is only one nil in the system return self" |
|
126 |
|
127 ^ self |
|
128 ! ! |
|
129 |
|
130 !UndefinedObject methodsFor:'printing & storing'! |
|
131 |
|
132 printString |
|
133 "return a string for printing myself" |
|
134 |
|
135 ^ 'nil' |
|
136 ! |
|
137 |
|
138 storeString |
|
139 "return a string for storing myself" |
|
140 |
|
141 ^ 'nil' |
|
142 ! ! |