Problems with Collection again.
Richard A. O'Keefe
ok at cs.otago.ac.nz
Tue Feb 4 03:11:21 UTC 2003
Janet Abdul-Karim <jn_karim at yahoo.com> wrote:
I made an instance of collection and trying to print out what is
in the collection. The way I coded seems to only print out the last
obect that I added.
We're missing a lot of context here.
Object subclass: #Portfolio
instanceVariableNames: 'accounts '
All I'm concerned with here is 'accounts'.
There is other information one might have about a portfolio,
such as who owns it, who manages it, its current value, &c.
portfolio:= SortedCollection new.
portfolio sortBlock:[:x :y | x name < y name].
portfolio add: aAccount.
This is confusing. A portfolio is not an account, and adding an account
is not the same as setting a portfolio.
Why is a SortedCollection used? SortedCollections are costly (one might
even say _very_ costly) to update. A variant of SortedCollection using
some kind of balanced binary search tree might be nice to have, but
SortedCollection itself is not such a data structure.
Let's use self-encapsulation to access 'accounts',
and within that, let's use lazy initialisation.
This way, the rest of the system NEVER sees a nil account collection.
accounts ifNil: [
accounts := SortedCollection new.
accounts sortBlock: [:x :y | x name < y name]].
Now if we ask for (aPortfolio accounts size) we don't have to worry
^self accounts add: anAccount
Now thing slike (aPortfolio addAccount: anAccount) will work fine,
albeit slowly (order N).
code to print portfolio
portfolio isNil ifTrue:[Transcript show: 'Portfolio empty'].
ifFalse:[portfolio do:[:element | Transcript show: element name]].
***if you are wondering y i did not use isEmpty instead I tried and it was giving me errors turned out isNil worked just fine. That fact that I could not use isEmpty make me wonder is porfolio is really a collection.***
Why bother with this at all? Why not just "inspect" or "explore"
a Portfolio instance? Or do this:
aStream nextPutAll: 'a Portfolio '.
sep := $(.
self accounts do: [:each |
aStream nextPut: sep.
each name printOn: aStream.
sep := Character space].
aStream nextPut: $).
Transcript show: aPortfolio printString; cr.
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