Stéphane Ducasse wrote:
Welcome
Hi, I have one begginer question. It is may be simple, but it very baffles me.
I am reading Pharo by Example (great book btw, thanks!). I'm in chapter two where I'm creating Lights Out
game. There is this simple code http://pastebin.com/eQregZ35. What baffles me is line 10. I assign
"Block of code" to mouseAction variable of LOCell. In this Block, there is "self", that
obviously refers to LOGame object in that time. But when is this Block actualy EVALUATED (when I click on
Cell), "self" should be reffering to LOCell object, isn't it? If I inspect one LOCell, inspector
shows that it has instance variable
Here is a draft of a next chapter on block :)
But I should finish it :)
------------------------------------------------------------------------
But I want to add how block are implemented at the bye code level so it take
times because not that many people are helping, so I have to learn first.
Stef
Thanks Stef. A very enlightening read. Its has helped in an example
I'll relate for other neophytes, and in case there are any traps or
patterns I am missing.
I have been struggling with how to implement a bidirectional
relationship between two classes such that consistency is enforced.
Take for instance the following classes...
Object subclass: #Book instanceVariableNames: 'bookTitle library'
Object subclass: #Library instanceVariableNames: 'libraryName books'
I want both the 'books' and 'library' instvars to remain private -
meaning that I don't want the default accessors providing direct access
to either. Then a method like 'Library>>addBook: aBook' which can
update its internal state modifying the 'books' collection cannot update
the internal 'library' state of 'aBook' - without Book having a setter
method to directly change the 'library' instvar - which I want to avoid
having. Trying to resolve this led me into recursion hell with too much
cross checking and guarding code.
What I was wanting was a way to expose the private state of one object
to another object in a controlled manner. So now I think this might be
achieved like this...
Library>>addBook: aBook
aBook addToLibrary: self.
Book>>addToLibrary: aLibrary
aLibrary addBook: self withBackLink: [ :backlinkValue | library :=
backlinkValue ].
Library>>addBook: aBook withBackLink: setBacklinkBlock
books ifNil: [ books := OrderedCollection new ].
books add: aBook.
setBacklinkBlock value: self.
Now having done that, I think I missed an alternative implementation...
Library >> addBook: aBook
aBook addToLibrary: self withInternalCollection: books
Book>>addToLibrary: aLibrary withInternalCollection:
libraryInternalBooksCollection
libraryInternalBooksCollection add: self.
library := aLibrary.
Book>>addToLibrary: aLibrary
aLibrary addBook: self.
and I'm not really sure of the pros & cons of each approach. Thoughts
anyone?
