Comment 1.

�� You probably meant to write

�� �� tracks: aCollection

�� �� �� ^tracks := aCollection

Comment 2.

�� This is a poor design.�� As it is, any object can replace the tracks of an artist

�� with *anything*.�� And even without doing that, any object can add and remove

�� items to an artist's tracks, even if the added items are not Tracks.

�� There are a number of OO design principles, notably the Law of Demeter and

�� of course the GRASP patterns, which basically say "never mutate another

�� object's parts, ask IT to do the mutation."

�� I have come to regard the self-encapsulation "pattern" as an anti-pattern.

�� This is Smalltalk heresy, admittedly, but it doesn't so much break (real)

�� encapsulation as set it on fire, defenestrate it, and urinate on the

�� smouldering remains.

So this is the way I'd do it.

�� ��Object subclass: #Artist

�� �� ��instanceVariableNames: 'tracks'

�� �� ��methods for: 'initialising'

�� �� �� ��initialize

�� �� �� �� ��tracks := OrderedCollection new.

�� �� �� �� ��^self

�� �� ��methods for: 'checking'

�� �� �� ��invariant

�� �� �� �� ��^(tracks isMemberOf: OrderedCollection) and: [

�� �� �� �� �� ��tracks allSatisfy: [:each | each isKindOf: Track]]

�� �� ��methods for: 'accessing tracks'

�� �� �� ��addTrack: aTrack.

�� �� �� �� ��tracks add: aTrack.��

�� �� �� �� ��^track

�� �� �� ��tracksDo: doBlock

�� �� �� �� ��tracks do: doBlock

with no way for outside code to accesss 'tracks' directly.

On Thu, 25 Jul 2019 at 02:47, sergio ruiz <sergio.rrd@gmail.com> wrote:

I'm implementing an instance variable as an OrderedCollection, and am doing something idiotic.

I have an Artist class.

An Artist can have many tracks:

tracks
�� ^ tracks ifNil: [ self tracks: OrderedCollection new ]

tracks: anObject
�� tracks := anObject ��

Doing something like:

a := Artist new.
t := Track new.
a tracks add: t

Gives me the error:

Artist(Object)>>doesNotUnderstand: #add:

Once I get past that error, which will evaluate `a tracks`, I can run this.

I get why it works the second time, but I don't get why it thinks the instance of Artist is the receiver of add: on the first run.

Thanks!

----
peace,
sergio
photographer, journalist,��visionary

Public Key:��http://bit.ly/29z9fG0
#BitMessage BM-NBaswViL21xqgg9STRJjaJaUoyiNe2dV
http://www.codeandmusic.com
http://www.twitter.com/sergio_101
http://www.facebook.com/sergio101