[Newbies] Enumeration type implementation

[Ralph Johnson]

That is not bad.   However, EpcimCurrency needs more behavior on the
instance side.   In particular, a currency should know both its name
and its description.   i think "value" is just the name.   The
dictionary should map names to currencies instead of names to strings
(or descriptions), and the instance should have instance variables
"name" and "description" instead of "value".   If you do it this way
then there will only be one instance of each currency and checking for
equality will be very easy.  But the overall design is on target.

On Wed, Jan 4, 2012 at 5:21 AM, Ben Coman <btc at openinworld.com> wrote:
> (Resending since it didn't show up on the list overnight)
>
> What is the best way to implement "enumerations" in Smalltalk. For instance,
> for a UML definition of...
> <<enumeration>> Currency
>  <<enum>> USD   'US dollar'
>  <<enum>> EUR   'Eueropean euro'
>  <<enum>> AUD    'Australian dollar'
>
> here is my guess, consisting of 2 instance side methods and 3 class side
> methods...
> -------------------------
> Object subclass: #EpcimCurrency
>  instanceVariableNames: 'value'
>  classVariableNames: ''
>  poolDictionaries: ''
>  category: 'IEC61970-Domain-Enumerations'
>
> EpcimCurrency >> value: aCurrency
>  ( (self class) validate: aCurrency) ifTrue:
>      [ value := aCurrency
>      ].
>
> EpcimCurrency >> value
>  ^value
> -----------------------------------
>
> EpcimCurrency class
>  instanceVariableNames: 'enums'
>
> EpcimCurrency class >> validate: aString
>  enums ifNil: [ self initialize ].
>  ^ enums includesKey: aString.
>
> EpcimCurrency class >>  enums   "for displaying in pulldown menus"
>  enums ifNil: [ self initialize ].
>  ^enums copy
>
> EpcimCurrency class >> initalize
>  (enums := Dictionary new)
>              add: 'USD'-> 'US dollar' ;
>              add: 'EUR'-> 'European euro' ;
>              add: 'AUD'-> 'Australian dollar' ;
>              add: 'CAD'-> 'Canadian dollar' ;
>              add: 'CHF'-> 'Swiss francs' ;
>              add: 'CNY'-> 'Chinese yuan renminbi' ;
>              add: 'DKK'-> 'Danish crown' ;
>              add: 'GBP'-> 'British pound' ;
>              add: 'JPY'-> 'Japanese yen' ;
>              add: 'NOK'-> 'Norwegian crown' ;
>              add: 'RUR'-> 'Russian ruble' ;
>              add: 'SEK'-> 'Swedish crown' ;
>              add: 'INR'-> 'India rupees' ;
>              add: 'other'-> 'Another type of currency' .
> ----------------------
> Examples
>  " (EpcimCurrency new value: 'AUD' ) value inspect  "      ----> 'AUD'
>  " (EpcimCurrency new value: 'XXX') value  inspect  "      ----> nil
>  " EpcimCurrency initialize  "
>  " EpcimCurrency enums inspect "   ---> aDictionary
> ------
> The other way I thought might be like `Color blue`, but I'm not sure what is
> gained.
>
> Your feedback would be appreciated.
>
>
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