[Newbies] subclasses detect

[gruntfuttuck]

Thank you, that was very clear and helpful :-)


David Mitchell-10 wrote:
> 
> The message #subclasses returns a collection of Class objects
> The message #detect: returns the first object in that collection that
> matches the criteria in the block
> 
> Since detect is the last message sent before the return, one class
> object will be returned.
> 
> If more than one matches, the code will never know, since detect:
> returns on the first match. It won't evaluate to find the other match.
> That is, it short circuits the iteration.
> 
> If you want to return a collection of matches, send the #select:
> message instead of #detect:.
> 
> Nothing to do with class instance variables (those are rare birds --
> misused as often as they are needed).
> 
> Also realize that the message isn't "subclasses detect". They are two
> separate messages. #detect: works with any collection. #subclasses
> returns a collection.
> 
> 
> 
> 
> On 7/31/07, gruntfuttuck <gruntfuttuck at gmail.com> wrote:
>>
>> Hello
>>
>> In the laser game tutorial by Stephan B Wessels I was intrerested by this
>> code:
>>
>> directionFor: aSymbol
>>         ^ self subclasses
>>                 detect: [:cls | cls directionSymbol = aSymbol]
>>
>> The code appears here at the bottom of the page:
>> http://squeak.preeminent.org/tut2007/html/038.html
>>
>> What I read this code as doing, in this example is: return an symbol
>> object
>> which is a sublass instance varable, if it is the same as aSymbol.
>>
>> What would happen if more than one subclass object had a match?
>>
>> Also how else can subclasses detect: be used? It looks very interesting.
>>
>> Grunt
>>
>>
>> --
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>>
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