On Sun, 20 Jan 2008 07:54:47 -0800, Ron Teitelbaum <[EMAIL PROTECTED]>
wrote:
Hi Blake,
There are a number of ways to initialize an object. Overridding #new is
an acceptable practice but normally this is done because you do not want
a new object created. For example if you wanted to have only one
instance of an object you might override #new to lookup your instance
and return that
instead.
Sure, for singletons. Good example.
Sometimes calling #new on class is a bad idea, either this class
shouldn't have instances, or there are other instance creation methods
that should be called instead. (We usually don't override new because
of other instance
creation methods but I can understand the argument if someone did)
Right. And while that's not necessarily ideal, I think it can be construed
as part of the price of knowing how to use an object. (Though I like
"contract-less" programming, do the degree it's possible.)
FishTank class>>newForGallons: numberOfGallons
"Create a fishTank that holds numberOfGallons"
aTank := super new. "call super to bypass error"
aTank numberOfGallons: numberOfGallons.
aTank calculateGlassForGallons.
aTank calculateTopSizeForGallons.
aTank calculateNumberOfLightsForGallons.
^aTank
Ok so this is kinda silly but I hope you get the idea. This is what
happens when I make stuff up on the spot!
Well, no, this is precisely the sort of situation I run into all the time.
"Gee, mister, I'd love to create an instance for ya, but I need to know
what kind of instance you want."
Ok so in most cases you can set your object up in #initalize
FishTank>>initialize
"set up default values for aFishTank"
self glassSides: OrderedCollection new.
self numberOfLights: 0 copy.
self tankShape: #rectangle
but you might want to change that setup during instance creation.
This also doens't solve your number of gallons issue. Which puts you in
the position of changing that number of gallons after the instance is
created.
You could also extend your class hierarchy to support different tanks.
Yes. This something that I'm getting used to.
Thanks, Ron.
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