[Newbies] Total newb...

[Marcin Tustin]

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 at 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 at lists.squeakfoundation.org [mailto:beginners-
> > bounces at lists.squeakfoundation.org] On Behalf Of Tony Giaccone
> > Sent: Tuesday, October 14, 2008 2:12 AM
> > To: beginners at 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
> >
> >
> > _______________________________________________
> > Beginners mailing list
> > Beginners at lists.squeakfoundation.org
> > http://lists.squeakfoundation.org/mailman/listinfo/beginners
>
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