author | Claus Gittinger <cg@exept.de> |
Mon, 16 Oct 2006 16:58:24 +0200 | |
changeset 10095 | 8b73365de8c3 |
parent 8681 | 38aa963476a5 |
child 11201 | 929ccb58d299 |
permissions | -rw-r--r-- |
6432 | 1 |
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COPYRIGHT (c) 2002 by eXept Software AG |
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All Rights Reserved |
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This software is furnished under a license and may be used |
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only in accordance with the terms of that license and with the |
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inclusion of the above copyright notice. This software may not |
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be provided or otherwise made available to, or used by, any |
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other person. No title to or ownership of the software is |
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hereby transferred. |
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" |
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"{ Package: 'stx:libbasic' }" |
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Notification subclass:#Query |
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instanceVariableNames:'' |
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classVariableNames:'' |
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poolDictionaries:'' |
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category:'Kernel-Exceptions' |
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! |
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!Query class methodsFor:'documentation'! |
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copyright |
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" |
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COPYRIGHT (c) 2002 by eXept Software AG |
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All Rights Reserved |
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This software is furnished under a license and may be used |
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only in accordance with the terms of that license and with the |
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inclusion of the above copyright notice. This software may not |
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be provided or otherwise made available to, or used by, any |
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other person. No title to or ownership of the software is |
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hereby transferred. |
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" |
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! |
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documentation |
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" |
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Query is an abstract superclass for queries. |
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A query is an exception which by default proceeds if unhandled and returns |
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a default value. |
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As a class based reimplementation, it replaces and obsoletes the old |
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QuerySignal instance based mechanism. |
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Note: |
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Query does not add/refine any functionality from its superclass. |
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It exists for the more descriptive class name only. |
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[author:] |
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Claus Gittinger |
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[see also:] |
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Warning Signal QuerySignal |
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" |
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! |
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examples |
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" |
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[exBegin] |
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Query answer:'hello' |
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do:[ |
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Transcript showCR:(Query query) |
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] |
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[exEnd] |
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an up-query from a deeply nested operation to a higher level: |
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the example below demonstrates that a Query is not an Error |
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(i.e. the Error-handler does not interfere with Queries) |
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[exBegin] |
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|zero| |
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zero := 0. |
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Query handle:[:ex | |
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Transcript showCR:'query'. |
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ex proceedWith:true |
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] do:[ |
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'nesting'. |
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[ |
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[ |
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Error handle:[:ex | |
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Transcript showCR:'some error: ' , ex errorString. |
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ex proceed |
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] do:[ |
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[ |
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1 // zero. 'an error which is caught in the handler'. |
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(Query query) == true ifTrue:[ |
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Transcript showCR:'query says: ok'. |
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] ifFalse:[ |
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Transcript showCR:'query says: no' |
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] |
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] value |
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] |
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] value |
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] value |
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] |
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[exEnd] |
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for lazy typists, a more compact interface for query-answerign |
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is also provided (which is also easier to read): |
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[exBegin] |
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Query answer:true do:[ |
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'nesting'. |
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[ |
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[ |
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(Query query) == true ifTrue:[ |
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Transcript showCR:'query says: ok'. |
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] ifFalse:[ |
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Transcript showCR:'query says: no' |
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] |
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] value |
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] value |
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] |
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[exEnd] |
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an up-query from a deeply nested operation, for which there |
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is no handler: |
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(notice, this would not work with normal signals, which would raise |
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another unhandled exception-exception; |
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also notice the == check #raise's return value being true, |
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instead of a simple ifTrue; this handles a nil-value from |
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the unhandled query) |
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[exBegin] |
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|zero| |
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zero := 0. |
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[ |
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'nesting'. |
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[ |
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[ |
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Error handle:[:ex | |
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Transcript showCR:'some error: ' , ex errorString. |
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ex proceed |
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] do:[ |
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[ |
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1 // zero. 'an error which is caught in the handler'. |
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(Query raise) == true ifTrue:[ |
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Transcript showCR:'query says: ok'. |
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] ifFalse:[ |
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Transcript showCR:'query says: no' |
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] |
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] value |
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] |
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] value |
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] value |
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] value |
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[exEnd] |
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counter-example, just to show that things would not work this way |
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with regular signals: |
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[exBegin] |
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|signal| |
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signal := Signal new. |
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'nesting deeply'. |
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[ |
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[ |
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[ |
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[ |
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[ |
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(signal raise) == true ifTrue:[ |
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Transcript showCR:'query says: ok'. |
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] ifFalse:[ |
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Transcript showCR:'query says: no' |
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] |
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] value |
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] value |
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] value |
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] value |
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] value |
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[exEnd] |
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except, by handling the unhandled exception |
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(but we think, that querySignals are easier to use and |
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better document the intent): |
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[exBegin] |
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|signal| |
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signal := Signal new. |
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'nesting deeply'. |
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[ |
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[ |
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[ |
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[ |
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[ |
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Signal noHandlerSignal handle:[:ex | |
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ex proceedWith:nil |
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] do:[ |
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(signal raise) == true ifTrue:[ |
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Transcript showCR:'query says: ok'. |
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] ifFalse:[ |
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Transcript showCR:'query says: no' |
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] |
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] |
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] value |
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] value |
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] value |
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] value |
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] value |
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[exEnd] |
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" |
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! ! |
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!Query class methodsFor:'initialization'! |
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initialize |
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NotifierString := 'Query'. |
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" |
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self initialize |
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" |
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! ! |
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!Query class methodsFor:'documentation'! |
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version |
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8681
38aa963476a5
Support for Block>>#on:do:on:do:
Stefan Vogel <sv@exept.de>
parents:
6433
diff
changeset
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^ '$Header: /cvs/stx/stx/libbasic/Query.st,v 1.11 2005-01-20 12:26:18 stefan Exp $' |
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! ! |
8681
38aa963476a5
Support for Block>>#on:do:on:do:
Stefan Vogel <sv@exept.de>
parents:
6433
diff
changeset
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6432 | 220 |
Query initialize! |