[Cuis-dev] How to use Events?

[Casey Ransberger]

Hey Juan, is the backticks thing specific to Cuis, or is this yet another magic feature of Smalltalk that I didn’t know about?

—Casey

> On Sep 9, 2019, at 6:04 AM, Juan Vuletich via Cuis-dev <cuis-dev at lists.cuis.st> wrote:
> 
>> On 9/9/2019 3:17 AM, Philip Bernhart via Cuis-dev wrote:
>> Hello,
>> 
>> I noticed that when I register events with when:send:to:with: with collections
>> as the with: paramater the contents of the collection the collection
>> becomes nil on the actually triggered event. Maybe that has something
>> todo with WeakMessageSend. Anyway an example tells better what I mean:
>> 
>> 
>> browserMorph
>>    setProperty: #editItemAction
>>    toValue: [:repository :record|
>>        | flashcardMorph card mapping |
>>        flashcardMorph _ FlashcardMorph new.
>>        card _ Flashcard new.
>>        card question: (record at: #question ifAbsent: '').
>>        card answer: (record at: #answer ifAbsent: '').
>>        
>>        card when: #changed
>>             send: #saveRecordMappingWith:
>>             to: browser
>>             with: {card. record}.
>> 
>>        flashcardMorph model: card.
>>        flashcardMorph showAnswer.
>>        flashcardMorph enableEditing.
>>        flashcardMorph openInWorld ].
>> 
>> Then in Flashcard there is a foo method which does:
>> self triggerEvent: #changed.
>> 
>> Here the {card. record} becomes for some reason (weak reference?) nil
>> and causes that the event isn't triggered. So #saveRecordMappingWith:
>> isn't called.
>> 
>> With simple datatypes like Integers this works, with static arrays this
>> seems to work too.
>> 
>> Maybe this style of doing that isn't the right one, maybe I'm using the
>> event system for things which it wasn't supposed to do.
>> 
>> Suggestions?
>> 
>> 
>> Thanks for your time,
>> Philip
> 
> Hi Philip,
> 
> I believe the event system uses WeakMessageSend in all Smalltalk dialects. Folks, please correct me if I'm wrong.
> 
> An easy way to fix the problem is to turn your collection into a literal, using backticks:
> 
>        card when: #changed
>             send: #saveRecordMappingWith:
>             to: browser
>             with: `{card. record}`.
> 
> 
> Cheers,
> 
> -- 
> Juan Vuletich
> www.cuis-smalltalk.org
> https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev
> https://github.com/jvuletich
> https://www.linkedin.com/in/juan-vuletich-75611b3
> @JuanVuletich
> 
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