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1 " |
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2 COPYRIGHT (c) 2012 by eXept Software AG |
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3 All Rights Reserved |
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4 |
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5 This software is furnished under a license and may be used |
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6 only in accordance with the terms of that license and with the |
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7 inclusion of the above copyright notice. This software may not |
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8 be provided or otherwise made available to, or used by, any |
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9 other person. No title to or ownership of the software is |
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10 hereby transferred. |
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11 " |
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12 "{ Package: 'stx:libbasic2' }" |
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13 |
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14 Object subclass:#CachedValue |
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15 instanceVariableNames:'value expirationTime computation validityDuration' |
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16 classVariableNames:'' |
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17 poolDictionaries:'' |
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18 category:'Kernel-Processes' |
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19 ! |
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20 |
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21 NotFoundError subclass:#ValueExpiredException |
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22 instanceVariableNames:'' |
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23 classVariableNames:'' |
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24 poolDictionaries:'' |
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25 privateIn:CachedValue |
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26 ! |
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27 |
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28 !CachedValue class methodsFor:'documentation'! |
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29 |
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30 copyright |
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31 " |
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32 COPYRIGHT (c) 2012 by eXept Software AG |
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33 All Rights Reserved |
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34 |
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35 This software is furnished under a license and may be used |
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36 only in accordance with the terms of that license and with the |
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37 inclusion of the above copyright notice. This software may not |
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38 be provided or otherwise made available to, or used by, any |
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39 other person. No title to or ownership of the software is |
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40 hereby transferred. |
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41 " |
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42 ! |
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43 |
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44 documentation |
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45 " |
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46 Instances of CachedValue can be used for values which are costly to evaluate, |
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47 but which can be cached for some time. |
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48 For example, when asking a source code repository for the set of symbolic names, |
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49 this query takes a few seconds (a CVS roundtrip). However, this information can easily |
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50 be cached and remembered for some time (say 30seconds or so), to speed up followup |
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51 repository operations. |
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52 You may find more similar uses of this class. |
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53 |
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54 [author:] |
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55 Claus Gittinger |
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56 |
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57 [instance variables:] |
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58 value ..................... the computed (cached value) |
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59 expirationTime ............ timeStamp, when this value becomes obsolete |
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60 validDuration ............. timeDuration, how long a computed value remains valid |
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61 computation ............... a computation block, to recompute the value. |
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62 |
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63 [class variables:] |
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64 |
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65 [see also:] |
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66 |
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67 " |
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68 ! |
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69 |
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70 examples |
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71 " |
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72 [exBegin] |
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73 |cv exceptionRaised didCompute| |
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74 |
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75 didCompute := false. |
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76 cv := CachedValue compute:[didCompute := true. Date today dayOfWeek] validityDuration:(2 seconds). |
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77 self assert:(cv isValid not). |
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78 self assert:(didCompute not). |
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79 self assert:(cv value = Date today dayOfWeek). |
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80 self assert:(cv isValid). |
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81 self assert:(didCompute). |
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82 |
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83 Delay waitForSeconds:3. |
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84 didCompute := false. |
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85 self assert:(cv isValid not). |
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86 self assert:(didCompute not). |
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87 self assert:(cv value = Date today dayOfWeek). |
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88 self assert:(cv isValid). |
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89 self assert:(didCompute). |
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90 [exEnd] |
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91 [exBegin] |
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92 |cv exceptionRaised| |
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93 |
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94 cv := CachedValue value:123 expirationTime:(Timestamp now + 2 seconds). |
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95 self assert:(cv isValid). |
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96 Delay waitForSeconds:3. |
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97 self assert:(cv isValid not). |
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98 |
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99 exceptionRaised := false. |
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100 ValueExpiredException handle:[:ex | |
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101 exceptionRaised := true. |
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102 ] do:[ |
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103 cv value |
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104 ]. |
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105 self assert:exceptionRaised. |
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106 [exEnd] |
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107 " |
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108 ! ! |
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109 |
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110 !CachedValue class methodsFor:'instance creation'! |
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111 |
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112 compute:actionBlock validityDuration:aTimeduration |
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113 "return a 'self computing' cachedvalue, which ceases to be valid aTimeduration after |
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114 it has computed its value. |
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115 If asked again for a value, it will automatically recompute the value." |
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116 |
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117 ^ self new |
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118 compute:actionBlock validityDuration:aTimeduration |
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119 ! |
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120 |
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121 value:valueArg expirationTime:aTimestamp |
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122 "return a 'one shot' cachedValue, which ceases to be valid at expirationTime. |
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123 If asked for the value after that, an exception is raised |
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124 (i.e. it does not automatically recompute a value)" |
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125 |
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126 ^ self new |
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127 value:valueArg expirationTime:aTimestamp |
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128 ! ! |
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129 |
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130 !CachedValue methodsFor:'accessing'! |
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131 |
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132 compute:computationBlock validityDuration:aTimeduration |
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133 computation := computationBlock. |
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134 validityDuration := aTimeduration |
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135 ! |
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136 |
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137 expirationTime:something |
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138 expirationTime := something. |
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139 ! |
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140 |
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141 value |
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142 "return my value. If not yet computed or expired, recompute using the computation block. |
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143 Otherwise return the cacehdValue" |
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144 |
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145 self isValid ifFalse:[ |
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146 validityDuration isNil ifTrue:[ |
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147 ValueExpiredException raiseRequestWith:self. |
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148 ^ nil |
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149 ]. |
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150 self computeCachedValue |
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151 ]. |
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152 ^ value |
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153 ! |
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154 |
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155 value:valueArg expirationTime:aTimestamp |
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156 value := valueArg. |
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157 expirationTime := aTimestamp |
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158 ! ! |
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159 |
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160 !CachedValue methodsFor:'private'! |
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161 |
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162 computeCachedValue |
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163 expirationTime := Timestamp now + validityDuration. |
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164 value := computation value. |
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165 ! ! |
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166 |
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167 !CachedValue methodsFor:'queries'! |
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168 |
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169 isValid |
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170 "true if the cached value is still valid" |
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171 |
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172 expirationTime notNil ifTrue:[ |
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173 expirationTime > Timestamp now ifTrue:[ |
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174 ^ true |
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175 ]. |
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176 expirationTime := nil. |
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177 ]. |
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178 ^ false |
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179 ! ! |
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180 |
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181 !CachedValue::ValueExpiredException class methodsFor:'documentation'! |
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182 |
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183 documentation |
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184 " |
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185 raised when a cachedValue has expired |
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186 " |
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187 ! ! |
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188 |
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189 !CachedValue::ValueExpiredException class methodsFor:'initialization'! |
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190 |
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191 initialize |
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192 NotifierString := 'value expired'. |
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193 ! ! |
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194 |
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195 !CachedValue class methodsFor:'documentation'! |
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196 |
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197 version |
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198 ^ '$Header: /cvs/stx/stx/libbasic2/CachedValue.st,v 1.1 2012-10-31 11:59:16 cg Exp $' |
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199 ! |
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200 |
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201 version_CVS |
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202 ^ '$Header: /cvs/stx/stx/libbasic2/CachedValue.st,v 1.1 2012-10-31 11:59:16 cg Exp $' |
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203 ! ! |
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204 |
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205 CachedValue::ValueExpiredException initialize! |