[Newbies] subclasses detect

[gruntfuttuck]

Thanks Steve, loving the tutorial. I wouldn't have given squeak another try
if it wasn't for your fabulous tutorial. 

My Girlfriend asked my what I was thinking about, after sex, the other day.
I didn't dare tell her, squeak code, so I said, our new home that we are
getting together. 




Steve Wessels wrote:
> 
> David's message is excellent.  The idiom used by this method is useful to
> understand.  I actually make a point of describing it's role as a
> substitution for a Case statement in a section just a few pages later in
> the Tutorial.  Check out page 048A.html 
> 
> - Steve
> 
> Sent from my iPhone
> 
> On Jul 31, 2007, at 4:00 PM, gruntfuttuck <gruntfuttuck at gmail.com> wrote:
> 
> 
> 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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