subclasses detect
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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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Its returning the actual matched class object. Not a symbol.
- Steve Sent from my iPhone On Jul 31, 2007, at 3:14 PM, gruntfuttuck <[hidden email]> 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. _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners ____________________________________________________________________________________ Take the Internet to Go: Yahoo!Go puts the Internet in your pocket: mail, news, photos & more. http://mobile.yahoo.com/go?refer=1GNXIC _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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In reply to this post by gruntfuttuck
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 <[hidden email]> 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. > > _______________________________________________ > Beginners mailing list > [hidden email] > http://lists.squeakfoundation.org/mailman/listinfo/beginners > Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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Thank you, that was very clear and helpful :-)
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In reply to this post by gruntfuttuck
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 <[hidden email]> 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 <[hidden email]> 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. _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners -- View this message in context: http://www.nabble.com/subclasses-detect-tf4196202.html#a11935026 Sent from the Squeak - Beginners mailing list archive at Nabble.com. _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners ____________________________________________________________________________________ Boardwalk for $500? In 2007? Ha! Play Monopoly Here and Now (it's updated for today's economy) at Yahoo! Games. http://get.games.yahoo.com/proddesc?gamekey=monopolyherenow _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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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.
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In reply to this post by gruntfuttuck
My God, that's funny.
Thank you for your kind words. Squeak has a special place in my "heart" too. - Steve Sent from my iPhone On Jul 31, 2007, at 5:33 PM, gruntfuttuck <[hidden email]> wrote: 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 <[hidden email]> 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 <[hidden email]> 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. _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners -- View this message in context: http://www.nabble.com/subclasses-detect-tf4196202.html#a11935026 Sent from the Squeak - Beginners mailing list archive at Nabble.com. _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners ____________________________________________________________________________________ Boardwalk for $500? In 2007? Ha! Play Monopoly Here and Now (it's updated for today's economy) at Yahoo! Games. http://get.games.yahoo.com/proddesc?gamekey=monopolyherenow _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners -- View this message in context: http://www.nabble.com/subclasses-detect-tf4196202.html#a11936372 Sent from the Squeak - Beginners mailing list archive at Nabble.com. _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners ____________________________________________________________________________________ Pinpoint customers who are looking for what you sell. http://searchmarketing.yahoo.com/ _______________________________________________ Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
Re: subclasses detect
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Hi Steve,
I think that this tutorial is great. I would like to make a translation to Spanish for my students later this year. Have you consider releasing it under a Creative Commons license (or something similar) to make derivated works of it (like translations)? Cheers and thanks for your tutorial, Offray Steve Wessels escribió: > My God, that's funny. > > Thank you for your kind words. > > Squeak has a special place in my "heart" too. > > - Steve > > Sent from my iPhone > > On Jul 31, 2007, at 5:33 PM, gruntfuttuck <[hidden email]> wrote: > > > 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 <[hidden email]> 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 <[hidden email]> 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. > > _______________________________________________ > Beginners mailing list > [hidden email] > http://lists.squeakfoundation.org/mailman/listinfo/beginners > > _______________________________________________ > Beginners mailing list > [hidden email] > http://lists.squeakfoundation.org/mailman/listinfo/beginners > > > > Beginners mailing list [hidden email] http://lists.squeakfoundation.org/mailman/listinfo/beginners |
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