[Cuis] #when:send:to:

[Juan Vuletich]

On 16/11/2015 10:50 p.m., Dan Norton wrote:
> On 16 Nov 2015 at 21:11, Juan Vuletich wrote:
>
>> Hi Dan,
>>
>> On 13/11/2015 02:58 p.m., Dan Norton wrote:
>>> Hello Everyone,
>>>
>>> The following repo contains before and after examples of replacing
>> the Dependency
>>> Mechanism with the Observer Pattern:
>>>
>>> 	https://github.com/dhnorton/Cuis-Smalltalk-light
>>>
>>> Please take a look at this and tell me what needs to change. I'm
>> trying to supply an example
>>> of the Observer Pattern so that others might use #when:send:to:
>> with less difficulty than I
>>> experienced. There may be better examples but I picked one from
>> the Blue Book.
>>> It seems that #when:send:to: is necessary but not sufficient as a
>> replacement for the
>>> Dependency Mechanism. In this example, it replaced #addDependent:,
>> not #changed or
>>> #update and I am still not comfortable with how to choose the
>> parameters. This may be an
>>> example of the difficulty in explaining the obvious, I'm not sure
>> :-)
>>> The #changed method was replaced with #triggerEvent: with a symbol
>> argument which is
>>> referred to in one of the arguments of #when:send:to: and that's
>> the only constraint AFAICT.
>>> The #update: method was retained, as a convenience; it also needs
>> to agree with one of the
>>> arguments of #when:send:to: and could have been different.
>>>
>>> Please tell me if any of this is wrong. Thanks.
>>>
>>>    - Dan
>> I think the idea of #when:send:to: is to use event names and actions
>> that make sense to your model (and not #changed and #update:). For
>> instance, in Example2>>#lights:, I would change the line:
>>
>>           eachLight when: #changed send: #update: to: dependentLight
>> with: self
>>
>> to read:
>>
>>           eachLight when: #turnedOn send: #turnOff to:
>> dependentLight
>>
>> And, in #turnOn, make it do:
>>
>>           self triggerEvent: #turnedOn
>>
>>
>> Doesn't this read better?
>>
> +2
> ...because yes, it reads better, but there's more:
>
> 	#when:send:to: replaces #when:send:to:with:
>
> 	in Light2, #update: goes away, with a little factoring
>
> The #triggerEvent: arg is changed to #turnedOn. This is elegant.
>
>   - Dan
>

Yes! And this way, 'senders' and 'implementors' take you right to the spot.

Cheers,
Juan Vuletich

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