Hi Matthias,

I don't know. Maybe the question was a bit unspecific, or I was a bit too tired (never try to answer questions before the first cup of coffee). Looking at his e-mail again, I think you're right. But he might pick up something interesting from my gibberish anyway. :-)

Best,

Michael

Hi Tony,

But what I really was looking for is

Given a set, how do I determine

1. If an object is a member of he set.

use aSet includes: anElement. As you noted, that requires equality to work.

2. How do I specify when two objects are equal? Is part of this.

In Smalltalk, you use = where you would use equals() in Java. The same rule applies: if you override = you sould also override the method hash.

You can look at the implementation of includes: in class Collection:

includes: anObject "Answer whether anObject is one of the receiver's elements."

^ self anySatisfy: [:each | each = anObject]

That confirms that = is the important method :-)

Cheers

Matthias

Obviously two objects which have the same address which I think in smalltalk is == operator are the same object..

but what if I want equality to be based on the value of some internal class value.

Maybe I'm thinking too much like a java programmer.

Tony

On Oct 14, 2008, at 2:56 AM, Matthias Berth wrote:

...

Hi Michael,

I think Tonys model of the game is like this:

A Player throws a hand. That can be any of "rock", "scissors", or "paper". Now someone (a Game object?) has to check if the player did not make a mistake, say by throwing a "well". The set of legal throws (in this game, anyway) is somehow defined by Tony. So the Game object checks if the throw is an element of the set of legal throws.

Am I describing this correctly, Tony?

Cheers

Matthias

On Tue, Oct 14, 2008 at 8:45 AM, Michael Haupt mhaupt@gmail.com wrote:

...

Hi Tony,

On Tue, Oct 14, 2008 at 8:11 AM, Tony Giaccone tony@giaccone.org wrote:

...

validHands := Set new. validHands add: Rock new; add Paper new; add Scissors new.

Assume I have a player object which responds to the method throwsAHand with an instance of Rock Paper or Scissors.

how do I craft

validHands contains: aPlayer throwsAHand

'ere, how about this:

validHands anySatisfy: [ :elem | elem respondsTo: #throwsAHand ]

Collection >> #anySatisfy: takes a block and evaluates it for all the elements in the collection. It returns true if the block evaluates to true for any of the elements, and false otherwise.

Object >> #respondsTo: accepts a symbol (!) denoting a message name and returns true if the object in question understands that message.

Did I make clear what the above code does?

Best,

Michael _______________________________________________ Beginners mailing list Beginners@lists.squeakfoundation.org http://lists.squeakfoundation.org/mailman/listinfo/beginners

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For C programmers, another way to look at blocks is that it is like passing a function pointer, except that instead of specifying the address of a function that you wrote elsewhere, you just write the text of the function.

On 10/14/08, Ron Teitelbaum Ron@usmedrec.com wrote:

Hi Tony,

You stumbled on one of the most powerful features of Smalltalk. The Block (See BlockContext). Blocks are a contextual memory space. They can be passed around and do all sorts of great things that Smalltalk programmers take for granted.

The basic form is [] this is a no argument, no code block. Pretty boring cause it does nothing.

A more advanced form is ['hello'] which is a block with a literal string. Still pretty boring. But at least you can get the string out of the block by aBlock := ['hello']. ^aBlock value.

A bit more advanced: [:arg | 'Hello ', arg] has an argument. Now you can do ^aBlock value: 'Ron'.

You can have more arguments [:arg1 :arg2 | 'Hello ', arg1, ' ', arg2].

Now you can do ^aBlock value: self firstName value: self lastName.

Even more complicated is: | isLoggedIn |

isLoggedIn := true.

[:arg | 'Hello ', arg, ' you are ', (isLoggedIn ifTrue: [''] ifFalse: [' not']), ' logged in']

Now you can do ^aBlock value: 'Ron'. From anywhere and the block remembers the context from where it was created. Pretty cool huh.

The regular select uses a block too:

self select: [:anItem | anItem isBlue]

which uses a do that uses a block

self do: [:anElement | aBlock value: anElement) ifTrue ... ]

Blocks are certainly a good thing to learn.

Happy Coding, Ron Teitelbaum

...

-----Original Message----- From: beginners-bounces@lists.squeakfoundation.org [mailto:beginners- bounces@lists.squeakfoundation.org] On Behalf Of Tony Giaccone Sent: Tuesday, October 14, 2008 2:12 AM To: beginners@lists.squeakfoundation.org Subject: [Newbies] Total newb...

Ok, so I'm really new to smalltalk. I've done a few basic tutorials and have a simple understanding of the syntax. My pervious programing experience is mostly java/C with a bit of Objective C in the mix.

I'm trying to figure out how to do what seems like a simple thing.

I have a set, I'd like to find out if an object exists in the set.

In a general form. Let's use the a relatively simple case.

Assume I have classes Rock Paper and Scissors.

validHands := Set new. validHands add: Rock new; add Paper new; add Scissors new.

Assume I have a player object which responds to the method throwsAHand with an instance of Rock Paper or Scissors.

how do I craft

validHands contains: aPlayer throwsAHand

I know that contains: takes a block, and that this isn't correctly done.. but I'm trying to get the a handle on how to do this. The intent is to return a boolean, that indicates if the object the player threw is in the Set of valid objects that can be thrown.

Tony

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