20 Mar
2003
20 Mar
'03
6:11 p.m.
"Visitor
(...)
Discussion
Is this object oriented design?
At first glance, the Visitor pattern seems contrary to classic
object-oriented design.
"(...Something how you normally would do it without using the
visitor-pattern)"
However, there are a couple of downsides to this approach. First,
nobody wants
to - or does - talk about this in the object-oriented literature, but
dispersing the draw code
all over the class hierarchy is problematic from a program
understanding perspective."
Why? Don't I do that all the time?
" (...)
Second, when we distribute the responsibility and implementation of an
operation involving the graphic element classes to each class, it's
harder to add a new
operation. Doing so means adding a new method to every Geometric class.
Hence, this solution is better when the set of operations is basically
static."
(Design Patterns Smalltalk Companion)
Hey, we have class-extensions.
I remain unconvinced/undecided about the visitor-pattern, is it
another C++-Legacy?
Markus
Am Donnerstag, 20.03.03 um 13:37 Uhr schrieb Alexandre Bergel:
Okay sorry.
I am a kind of ashamed by this email. A real newbies mistake.
The correct way is to create a new Visitor inheriting from
VisitorRenderer*
In short the responsability of adding a page in the
PagesVisitedComponent belongs to the visitor and __not__ to the page,
as I first thought.
I will never make a such mistake, I promise :-)
Alexandre
On Thu, Mar 20, 2003 at 12:14:26PM +0100, Alexandre Bergel wrote:
[For Lukas and Steph] Last time with Gabriela we
have coded together
the Page visited component. We get stuck because we put a method such
as:
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Page>>accept: aVisitor
aVisitor acceptPage: self.
(self template propertyAt: #visitedPages) addPage: self
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
The result was the component reference all the pages of the wiki,
even if we display it or not.
I understood why. A page is not only visited by a rendered visitor,
by also by VisitorReferences.
So, a code something like works:
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Page>>accept: aVisitor
aVisitor acceptPage: self.
(aVisitor isKindOf: VisitorRenderer) ifTrue: [
(self template propertyAt: #visitedPages) addPage: self]
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Okay, now I have some questions:
1- What is the meaning of VisitorReferences,
2- What is the meaning of TemplateReferences
The both question are nearly the same, but I do not have so much time
to dive in the code.
My guess is it is needed for the saving mechanism...
and the last one:
3- A page should get a reference so the component for being
referenced when visited. In the previous code "self template" return
the __root__ of the template structure. So, our first idea was to add
a property in the root for referencing the component. But, we need to
modify such method. And I admit it is not homogenous :-)
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
defaultTemplate
| ans v |
ans := TemplateRoot
child: (TemplateContainerRows new
add: (TemplateStringTitleWiki new);
add: (TemplateContainerColumns new
add: (TemplateStructuresPath new);
add: (TemplateHeatBox new);
yourself);
add: (TemplateContainerColumns new
add: (TemplateContainerRows new
add: (TemplateActionsCustom new);
add: (TemplateStructuresReferences new);
add: (v := TemplateVisitedPages new);
yourself);
add: (TemplateContainerRows new
add: (TemplateStringTitleAction new);
add: (TemplateStringContent new);
yourself);
yourself);
add: (TemplateStringAbout new);
yourself).
ans propertyAt: #visitedPages put: v. "<=======Here a new line
!!!!"
^ ans
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Lukas, tell me what do you think about this way for letting a page to
access a component...
I think it is not bad...
Alexandre
--
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Alexandre Bergel http://www.iam.unibe.ch/~bergel
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--
_,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
Alexandre Bergel http://www.iam.unibe.ch/~bergel
^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.