Class: HandlerCollection

• Inheritance
• Description
• Instance protocol
  • adding
  • private
  • save evaluation

Inheritance:

   Object
   |
   +--Collection
      |
      +--SequenceableCollection
         |
         +--OrderedCollection
            |
            +--HandlerCollection

Package:

stx:libbasic2

Category:

Kernel-Exceptions

Version:

rev: 1.6 date: 2021/01/20 14:33:02

user: cg

file: HandlerCollection.st directory: libbasic2

module: stx stc-classLibrary: libbasic2

Description:

A HandlerCollection allows a group of unrelated signals to be handled
by individual handlers - their evaluation is equivalent to a corresponding
number of nested signal handlers, but somwehat easier to program.
In the real world, handlerCollections are seldom needed and actually currently
not used by the system.

copyright
COPYRIGHT (c) 1994 by Claus Gittinger
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Instance protocol:

 on: aSignal handle: aHandler

add a signal<->handler pair to the receiver collection

 from: start to: stop handleDo: aBlock

this method recursively sets up a bunch of nested
handlers, and finally evaluates the argument, aBlock

 handleDo: aBlock

evaluate the argument, aBlock.
If any of the signals in the receiver is raised during evaluation,
evaluate the corresponding handleBlock from the receiver,
passing it an Exception argument.
The handler may decide how to react to the signal by sending
a corresponding message to the exception (see there).
If none of the signals is raised during evaluation, return the
value returned by aBlock.

Usage example(s):

|h num| h := HandlerCollection new. h on:(Number divisionByZeroSignal) handle:[:ex | 'division by zero' printNL. ex proceed]. h on:(Object haltSignal) handle:[:ex | 'halt encountered ' printNL. ex proceed]. h on:(Float domainErrorSignal) handle:[:ex | 'domain error ' printNL. ex proceed]. h handleDo:[ num := 0. 'now dividing' printNL. 1 // num. 'now doing bad arcSin' printNL. num := 50. num arcSin. 'now halting' printNL. self halt. ]