Examples of exception handling The follow examples show how to handle various situations: Example: printing an object "Assume that printString will call self error: if it encounters an error condition." | anObject | [ anObject printString ] when: ExError do: [:signal | signal exitWith: [ 'Exception: ', signal argument, 'while printing a ', anObject class name ]. Example: trapping user break "Unbreakable code" [ 1000 timesRepeat: [ String new: 100000 ] ] when: ExUserBreak do: [:signal | System confirm: 'Caught user break'. signal resumeWith: nil ]. Example: growing a stack "Assume that a Stack class with a push: method exists in the application." (OverflowException := ExAll newChild) description: 'stack overflow'. [ aStack push: anInteger ] when: OverflowException do: [:signal | aStack grow. signal retry ]. Example: propagating a different exception | aDifferentException | (aDifferentException := ExAll newChild) description: 'this is a different exception'. [ 1 error: 'demonstration' ] when: ExError do: [:signal | aDifferentException signal ] Example: top-level loop | loopExitException | loopExitException := ExAll newChild. [ [true] whileTrue: [ "Body of loop; can only be exited by sending 'loopExitException signal'." (System confirm: 'Signal the loopExitException') ifTrue: [ loopExitException signal ]. "Create a doesNotUnderstandException." 1 error: 'This is for demonstration purposes' ] ] when: loopExitException do: [:signal | signal exitWith: 'bye' ] when: ExAll do: [:signal | System message: 'An Exception has occurred: ', signal description. signal retry ]. Example: close stream at end or on error "If an error occurs, it is reported normally, but aStream is closed first." | aStream | aStream := ReadStream on: 'This is a test'. [ [ aStream atEnd ] whileFalse: [ Transcript nextPut: aStream next ] ] atEndOrWhenExceptionDo: [ Transcript show: '...Closing the stream'. aStream close ]
