Category:Smalltalk: Difference between revisions

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<lang smalltalk>[ try block to be evaluated ] on: exception do:[:ex | handler code ]</lang>

the 'ex' argument to the hander provides detail information (where and why) and also allows control of how to ~~proceed~~ ~~out of~~ the handler (ex proceed, ex return, ex restart, ex reject).

the 'ex' argument to the hander provides detail information (where and why) and also allows control of how to continue after the handler (proceed, return, restart, reject).

The handler basically has the following options:

<br>The handler basically has the following options:

* ex return - return out of the try block

* ex restart - restart the try block

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* ex proceedWith: value - proceed after where the exception was raised (after a repair)

Exceptions may be specified to be nonProceedable, to protect code from proceeding handlers, where proceeding is not possible.

Exceptions form a hierarchy, so a handler will also catch any derived exceptions. If an exception is unhandled, the original exception info is packed up and an UnhandledException is raised~~. Thus~~ (similar to the handling of doesNotUnderstand:). The default handler for UnhandledException opens a debugger for the misbehaving thread (while usually other threads continue to operate as usual).

Exceptions form a hierarchy, so a handler will also catch any derived exceptions. If an exception is unhandled, the original exception info is packed up and an UnhandledException is raised (similar to the handling of doesNotUnderstand:). The default handler for UnhandledException opens a debugger for the misbehaving thread (while usually other threads continue to operate as usual).

Handlers can also be defined to handle a collection of non-related exceptions, by creating an exceptionSet: