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@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@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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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@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@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
-- View this message in context: http://www.nabble.com/subclasses-detect-tf4196202.html#a11934239 Sent from the Squeak - Beginners mailing list archive at Nabble.com.
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