[Newbies] How to create new exception

Michael van der Gulik mikevdg at gmail.com
Wed Oct 15 21:19:33 UTC 2008

On Wed, Oct 15, 2008 at 5:22 PM, Alex Chi <alex_chi99 at yahoo.com> wrote:

> Sorry for the that, I mean my problem is I put the exception in the wrong
> part of my program, so everytime I try to call it in the method it does not
> return the exception, so what i did was:
> 1. Create an new exception class, which is: FileNotFoundError
> Smalltalk.Core defineClass: #FileNotFound
>     superclass: #{Core.Error}
>     indexedType: #none
>     private: false
>     instanceVariableNames: ''
>     classInstanceVariableNames: ''
>     imports: ''
>     category: ''
> 2. I use that new exception to raise signal on a FileNotFoundError.
>     fileNotFound
>         ^FileNotFound raiseSignal: 'The file is not exist'

Which version of Smalltalk are you using? This doesn't look like Squeak to

If you want an Exception object, you could just return a new instance:

   ^ FileDoesNotExistException new.

Although this method is pretty pointless.

I think you're misunderstanding how Exceptions work; you need to do more
reading. I'm not sure if Smalltalk Exceptions are well documented anywhere,
but I do know that they work in a similar way to exceptions in other
programming languages such as Java or Python, so you could Google or get
books from a library that describe these.

Briefly, Exceptions are intended for handling situations where something
goes wrong. See "FileDoesNotExistException class>>example" for an example.


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