[Newbies] Re: I am a total beginner with some questions
ncellier at ifrance.com
Wed Apr 9 18:59:33 UTC 2008
Michael Haupt wrote:
> I wonder why no one has recommended the excellent "Squeak by Example"
> book yet... to get a hang of what programming in Squeak looks (and
> feels) like, you *really* ought to work your way through this book.
> It's available as a free PDF download: http://www.squeakbyexample.org/
> Now, on to your problem...
> On Wed, Apr 9, 2008 at 2:38 AM, kennellgr <cboneg5 at gmail.com> wrote:
>> I appreciate the help. I tried it out and it works. I have one problem
>> though. I created a method called "gdkDKeyDown" (gdk is my innitials so I
>> put it before my methods) and when I type gdkDKeyDown in a workspace and
>> print it it says nil (it's supposed to say true or false) how do I make it
>> return a value?
> In Smalltalk (and hence, also in Squeak), you cannot simply invoke a
> method by typing its name and issuing "do it" or "print it" - instead,
> you send a message to an object. To be able to do that, you need to
> implement the method in some class so that instances of that class can
> actually understand the message (and effectively execute the method).
A little bit more explanations: Why this nil?
If you take a look further at a formal description of Smalltalk syntax,
you will see that this sentence:
can only be interpreted as a variable, and in this case an undeclared
variable (from the workspace, only global variables from the Smalltalk
SystemDictionary are visible, also as variables attached to the
workspace as explained below).
When you evaluate ("doIt") from a workspace, then such undeclared
variables are automatically declared as workspace variables.
And since no value has ever been assigned to this workspace variable, it
is initialized with an instance of UndefinedObject, that is nil (the
sole instance of UndefinedObject in fact).
When you think of it, the meaning is simply undefined, something like
the NULL pointer in other languages... except that in Smalltalk this is
just an object among other objects. Yes as if you could operate on the
NULL pointer without crashing the application with a segmentation fault.
Isn't it a nice property?
You now need to find to which object you should send the gdkDKeyDown
> Please look at "Squeak by Example"; I really feel you need to do that
> before you start. :-)
I strongly second Michael advice.
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