[Newbies] enumerated types

Michael van der Gulik mikevdg at gmail.com
Mon Oct 6 02:05:09 UTC 2008

On Mon, Oct 6, 2008 at 2:48 PM, Mark Volkmann <mark at ociweb.com> wrote:

> On Oct 5, 2008, at 8:38 PM, Michael van der Gulik wrote:
> What are you using enums for? I've never found I've needed them, often
> because the need for them can be refactored away and you end up with cleaner
> code.
> Often I just use symbols (i.e. #red, #blue, #green). These are generic
> descriptive names for thingies.
> I haven't used them yet in Smalltalk, but I'm thinking I'll have a need to
> verify that a value passed to a method is a member of a confined set. Maybe
> I should just test a symbol passed as an argument to a method to see if it's
> in an array of allowed symbols.

Well, there are simpler ways of doing that such as:

isMemberOfConfinedSet: anArg
    (ValidValues includes: anArg) ifFalse: [self error: 'foo'].

Where ValidValues is a class variable and a Collection of valid values.

Alternatively, a more Smalltalkish way that I don't like:

isMemberOfConfinedSet: anArg
    (anArg isSomething) ifFalse: [self error: 'foo'].

Where >>isSomething is implemented to return true on all objects that could
be a member. This method I find rather intrusive, especially if implemented
on core classes like Object and String, but does run very fast because a
simple method that just returns true has special optimisations in the VM.


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