On Thu, Jan 19, 2017 at 11:37 AM, Sven Van Caekenberghe <sven@stfx.eu> wrote:
The Traits would be cool to standardise the behaviour and to mark it as such (implicit documentation)

Exactly.��
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, however, Traits cannot add instance/class variables IIUC, that limits what they can do (and would make it more than one step).

Ok. So that's the difference between a Ruby mixin and a trait. That's a shame, I think what Ruby does with mixins is really nice because it a) results in less code to test, and b) makes hineritance chains more semantic - you only inherit to model spcialization, not to reuse features.

Cyril, many thanks! I know how to implement it and it is true that it is not much, but I had hoped to eliminate the code (and tests!) and use a standard feature if possible ;)

-- Siemen
��

> On 19 Jan 2017, at 11:33, Cyril Ferlicot D. <cyril.ferlicot@gmail.com> wrote:
>
> On 19/01/2017 11:23, Siemen Baader wrote:
>> Is there a trait to quickly create singletons in Pharo, along the way of
>> the Ruby Singleton mixin?
>>
>> https://ruby-doc.org/stdlib-1.9.3/libdoc/singleton/rdoc/Singleton.html
>>
>> (and ideally also observer/observable, which I am going to need next..)
>>
>> -- Siemen
>
> Hi!
>
> Singleton in Smalltalk are really easy so there is no Trait.
>
> You just need a class variable #UniqueInstance and those methods:
>
> current
>�� �� "Can also be named #default or #instance"
>�� �� �� ��^ UniqueInstance
>�� �� �� �� �� �� �� ��ifNil: [ UniqueInstance := self basicNew; initialize; yourself ]
>
> new
>�� �� �� ��^ self error: 'I am a Singleton. Use current to get my instance or
> reset my instance with a new project. Maybe explain why there is a
> Singleton because we should avoid them if possible.'
>
>
> Now for the observer pattern you have the Announcement framework in Pharo.
>
> I don't really have the time to explain but I think there is some doc on
> internet and on the help browser of Pharo. I found this:
> http://pharo.gemtalksystems.com/book/LanguageAndLibraries/announcements/
> (I did not read it so I don't know what it's worth)
>
> --
> Cyril Ferlicot
>
> http://www.synectique.eu
>
> 2 rue Jacques Pr��vert 01,
> 59650 Villeneuve d'ascq France
>